Influence Of Enhancement Oxygen Concentration On Solid Biomass Burning (repaired) [613724]

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POLITEHNICA UNIVERSITY OF BUCHAREST
FACULTY OF MECHANICAL ENGINEERING AND
MECHATRONICS
THERMOMECHANICAL, CLASSIC AND NUCLEAR EQUIPMENT

Influence of Enhancement Oxygen Concentration on
Solid Biomass Burning
First Scientific Report Submitted to the
Mechanical Engineering Department,
Doctorate of Engineering
Politehnica University of Bucharest
Romania

Author: Alaa Aldin Hussein Ali Al jawad

Doctoral Supervisor
Prof. Dr. Ing . PÎȘÃ LONEL

2 Table of Contents

Abstract ………………………….. ………………………….. ………………………….. ………………………….. …………………….. 3
Introduction ………………………….. ………………………….. ………………………….. ………………………….. ……………….. 4
Biomass classification ………………………….. ………………………….. ………………………….. ………………………….. …… 8
Woody Biomass ………………………….. ………………………….. ………………………….. ………………………….. ……. 8
Herbaceous Biomass ………………………….. ………………………….. ………………………….. …………………………. 8
Fruit and Aquatic Bi omass ………………………….. ………………………….. ………………………….. ………………….. 8
Solid Biofuel Standardization ………………………….. ………………………….. ………………………….. ……………………… 9
Combustion ………………………….. ………………………….. ………………………….. ………………………….. ………………. 10
Biomass combustion ………………………….. ………………………….. ………………………….. ………………………….. ….. 11
The biomass combustion process ………………………….. ………………………….. ………………………….. ……………… 11
DRYING ………………………….. ………………………….. ………………………….. ………………………….. ………………… 11
Pyrolysis ………………………….. ………………………….. ………………………….. ………………………….. ……………….. 13
Gasification ………………………….. ………………………….. ………………………….. ………………………….. …………… 15
Complete Combustion ………………………….. ………………………….. ………………………….. …………………………. 17
Review for research subject ………………………….. ………………………….. ………………………….. …………………….. 19
Conclusion ………………………….. ………………………….. ………………………….. ………………………….. ……………….. 28
Bibliography ………………………….. ………………………….. ………………………….. ………………………….. ……………… 29

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Abstract

In this research will investigate the effect of enhancing the concentration of oxygen in the air on the
efficiency of combustion in solid biomasses and the flue gases emission, and a review of a set of research and working papers. The purpose is to find the preferred method to obtain the highest
possible thermal efficiency, with minimal pollutant emissions.
Since the natural oxygen concentration in the atmosphere is 21%, a nd when the oxygen concentration
increases, the efficiency of combustion increase and conversely, pollution decreases, Oxygen
concentration may reach 99% as happens in welding and smelting processes and in some glass
melting furnaces, the amount of heat generated from it is as high as 3087 ° C with low emission.
The main idea is to increase the concentration of oxygen by specific percentages in the furnace to
burn solid biomasses and investigate its direct impact on raising the efficiency of the furnace and
calculating the pollution rate in the flue gases. This is done by inserting different levels of
concentrations from a source to generate or store oxygen on several types of solid biomasses in the
furnace.

4 Introduction

One of the greatest, challenges facing the world in the second millennium is global warming and air
pollution, or the greenhouse phenomenon, which causes global temperature rising. The globe becomes more like a glass box, to which the large quantities sunl ight enters and little amount exit.
The reasons for the warming of the planet earth are the increase in the percentage of greenhouse gases in the atmosphere, such as methane and carbon dioxide, as carbon dioxide absorbs heat from the sun's
rays, then relau nches it in the atmosphere, which increases the overall temperature of the earth.
The biggest sources of these emissions are fossil fuel burning products such as gas, coal, and oil.
Researchers and scientists are focusing on finding alternatives to fossil fuels. Hence, the study of
biofuels began with various types of liquid, gaseous, and solid, which can be an alternative to fossil fuels. Biofuels have been used throughout the ages since humans became familiar with the fire and
started using it in their d aily needs. One of the main problems of biofuels and biomass is the high rate
of pollutants emission in the flue gases.
Biomass fuels differ in many ways from the conventional fossil fuels used in combustion processes, such as coal. They often have high mo isture contents, lower heating values, and a variety of minor
constituents, such as chlorine, sulfur, phosphorus, nitrogen, and a variety of ash -forming metals.
These special properties of biomass fuels cause several challenges, but in many cases also prov ide
advantages, to their use in combustion processes. Design of the combustion devices and choice of
their operating parameters are very dependent on the detailed properties of the biomass fuel or fuels to be used. Often these challenges are connected to t he fate and chemistry of the many minor
constituents or impurities of the fuels
the use of low -grade fuels such as various biomasses is
increasing rapidly as an alternative to conventional fossil fuels. Biomass can be defined as organic
matter derived from living, or recently living organisms . [1]
The qualities and properties of biomasses vary a lot. Biomass has less carbon; more oxygen and a lower heating value than coal (see Fig. 1). The volatile content is considerably higher and the fixed
carbon content is lower for biomass compared to coal. Further, biomasses often have high moisture contents. Many challenges are related to the minor constituents or i mpurities contained in these fu els.
Biomasses have a variety of minor constituents, such as chlorine, sulfur, phosphorus, nitrogen, and a
variety of ash -forming metals (Fig. 2). This special properties of biomass fuels cause several
challenges to their use in combustion processes. One key point is to combin e/select fuels so that
problems associated with various elements are eliminated. For example, fuels with high potassium and chlorine contents may lead to problems with fouling and corrosion; however, these problems may be solved by co -firing fuels with hig h sulfur content. Design of the combustion devices and choice of
their operating parameters are very dependent on the detailed properties of the biomass fuel or fuels
to be used. Often these challenges are connected to the fate and chemistry of the many mi nor
constituents or impurities of the fuels. Figure 3 summarizes some of the chemistry -related challenges

5 in biomass combustion. Some of these challenges are similar to the ones in combustion systems using
conventional fuels such as coal or even oil. However, in biomass combustion, the phenomena and solutions needed may be very different. The chemical compositions of the biomasses influence the
extent and severity of the problems illustrated in Fig. 3. [1]

(Fig. 1). (a) Properties for various types of solid fuels ( daf, dry ash free basis; db, dry basis) , (b) van
Krevelen diagram of various fuels. [ 2],

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(Fig. 2) Ash forming elements in various biomass fuels (db, dry basis). [2],

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(Fig 3) Chemistry related challenges in biomass combustion. [1]
Fig. 3 requires a good understanding of the chemical behavior of the minor constituents and
impurities of the fuel during the combustion process and in the flue gases. Consequently, research
around problems caused by the minor constituents in the biomasses and waste -derived fuels has been
intense in the past ten years all over the world . [1]

8 Biomass classification
According to EN ISO, 17225- 1:2014 standard, biomass feedstock resources are distinguished into four specific
groups, namely woody, herbaceous, fruit and aquatic biomass. The standard also defines a general group,
that of bends and mixtures, which combines the material of various origins from the previous categories.
Blends are intentionally mixed bi ofuels, where mixtures are unintentionally mixed biofuels. [3]
Woody Biomass
Fruit biomass is the biomass from the parts of a plant which are from or hold seeds. Aquatic biomass
refers to plants that ha ve adapted to living in or on aquatic environments. Woody biomass, especially
forestry derived, is the most abundant type of solid biofuel which was used for thousands of years for heat production purposes. The first and most extensively exploited type of woody biomass, main regards feedstock derived
(a) As raw material from the forest, plantation, or other virgin wood (e.g. wood from forests, parks,
gardens, plantations, and from short -rotation forests and coppice),
(b) As wood by -products and wood residue s from industrial production (i.e. wood processing which
may be chemically treated or not),
(c) Used wood, derived from post -consumer wood waste; natural or merely mechanically processed
wood … [3]
Herbaceous Biomass
This group includes herbaceous material from the agricultural and horticultural sectors as well as
residues and by -products from food and herbaceous processing industry. Examples of herbaceous
biomass resources are herbaceous energy crop s grown specifically as biomass fuels (e.g. cereal crops,
sunflower or rapeseed, switch grass, sugarcane, maize) or by -products and residues derived from the
production of non -energy products (e.g. wheat straw, barley straw). Herbaceous biomass can also be
obtained from gardens, parks, and roadside maintenance.
Fruit and Aquatic Biomass
Fruit biomass refers to biomass feedstock obtained from trees, bushes, and herbs as well as fruit biomass material and vegetable residues which are leftover in the fruit and food processing industry,
respectively. An example of fruit biomass residue is olive oil residues which are produced during the olive oil production process .
The last group of biomass resource regards aquatic originated feedstock such as algae, water
hyacinth, lake, and sea weed.

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Solid Biofuel Standardization
In view of the rapidly increasing international trade of solid biofuels and the demand for continuous
improvement of the existing pretreatment methods and feedstock -to-biofuel conversion technolo gies,
the need for concise and unambiguous criteria for their classification has become imperative. The criteria are both in name and in measure physicochemical characteristics . [3]
The properties of th e processed feedstock play a key role in the performance of the pretreatment
methods as well as on the determination of the most suitable conversion process (McKendry 2002). The most important feedstock properties during biomass processing relate to:
1. The Moisture Content of biomass indicates the total amount of water in the material,
expressed as a percentage of the material’s weight (i.e. w -%). Moisture content can be
expressed in different bases, namely wet, dry, and dry -ash-free basis.
2. The Ash Content refers to the inorganic component of biomass and is usually expressed on a
dry basis.
3. The Volatile Matter is determined as the loss in mass, less than due to moisture when solid
biofuel is subject to partial pyrolysis under standardized conditions.
4. The Calorific Value Measurements the calorific value gives an indication of the energy
content of a material, released when burnt in air. Calorific value is usually expressed in terms
of the energy content per unit mass or volume (i.e. MJ/kg or MJ/l). The CV o f a fuel is
expressed in two forms, namely the gross calorific value of (GCV) or higher heating value (HHV) and the net calorific value (NCV), or lower heating value (LHV) In contrast to LHV
which is the most widely -used value for expressing the energy con tent
5. The C, H, N, S, O content for the definition of the CHN composition of the investigated solid
biomass, a known mass of a sample is burnt in oxygen under conditions such that it is
converted into ash and gaseous products of combustion, consisting mainl y of carbon dioxide,
water vapors, elemental nitrogen, and/or oxides of nitrogen. The various mass fractions of the gas stream are then determined quantitatively by appropriate instrumental gas -analysis
procedures.
6. Definition of Major and Minor Elements for major elements, the sample is digested in a
closed vessel by the help of reagents, temperature, and pressure. The digestion is either carried out directly on the fuel or on a 550 °C prepared ash. For minor elements, the analysis sample
is digested in a vessel made from a fluoropolymer using nitric acid, hydrogen peroxide, and
hydrofluoric acid in a microwave oven or a resistance oven or heating block. The digest is then diluted and the elements determined with suitable instruments.
7. Ash Melting Behavior a test piece made from prepared ash is heated up with a constant rate
and continuously observed. The temperature is initially raised to 550 °C or at a point which is minimum 150 °C below the expected shrinkage starting temperature, SST at a uniform rate
within the range of 3 °C/min to 10 °C/min. The temperatures at which characteristic changes
of the shape occur are recorded (i.e. shrinkage starting temperature, SST; deformation temperature, DT; hemisphere temperature, HT; and flow temperature, FT).
8. Mechanical Durability the mechanical durability of the tested sample is defined by
controlled shocks by the collision of pellets against each other and against the walls of a

10 specified rotating test chamber. The durability is calculated from the mass of sample
remaining after separation of abraded and fine broken particles.
9. Particle Size Distribution the particle size distribution of solid biofuels is defined through a
sample subjected to sieving through horizontally oscillating sieves, sorting the particles in
decreasing size classes by mechanical means. For the test, an appropriate number of either
circular or rectangular sieves with a minimum effective sieve area of 1200 cm2 are required .
[3]
10. Length and Diameter the length and diameter of solid biofuel pellets of a representative
sample of fuel pellets are measured by using a calliper. The length of a pellet is always
measured along the axis of the cylinder. The diameter is measured perpendicular to the axis.
11. Bulk De nsity for the definition of the bulk density of the raw material, as well as of the
processed pellets, the test portion is filled into a standard container of a given size and shape
and is weighed afterwards. Bulk density is calculated from the net weight per standard volume
and reported for the measured moisture content. [3]

Combustion

Combustion is the chemical term for a process known more commonly as burning. It is certainly one
of the earliest chemical changes noted by humans, at least partly because of the dramatic effects it has on materials. Today, the mechanism by which combustion takes place is well understood and is more correctly defined as a form of oxidation that occurs so rapi dly that noticeable heat and light are
produced
Combustion is a complex series of chemical reactions between fuel and oxidation accompanied by the production of heat or both heat and light in the form of glow or flame. It can be used as energy as
needed.
Fire (or combustion) also helps create technologies for industrial use. Combustion is the most
common method of energy conversion currently used. The major portion of power is generated from
coal- and natural -gas-burning power plants that produce steam, whi ch in turn drives electric
generators. These are known as external combustion (EC). This is our main subject in this study

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Fuel+O2 → Product+ Heat
Combustion usually occurs when a hydrocarbon reacts with oxygen to produce carbon dioxide
and water.
C+O2 = CO2
C+1/2 O2 =CO
CO+1/2 O2 =CO2
H2+1/2 O2=H2O
S+O2=SO2
In the more general sense Combustion involves a reaction between any combustible material and
an oxidizer to form an oxidized product.
Biomass combustion

The process of biomass combustion involves a number of physical/chemical aspects of high
complexity .The nature of the combustion process depends both on the fuel properties and the
combustion application. The combustion process can be divided into several general processes:
drying, pyrolysis, gasi fication and combustion. The overall combustion process can either be a
continuous combustion process or a batch combustion process, and air addition can be carried out
either by forced or natural draught.
The biomass combustion process
DRYING
Moisture will evaporate at low temperatures (100°C). Since vaporization uses the energy released from
the combustion process, it lowers the temperature in the combustion chamber, which slows down the
combustion process. The combustion process cannot be mai ntained if the wood moisture content
exceeds 60 per cent on a wet basis (w.b .)
Moisture content
w.b. =mass of water /mass of moisture on sample
d.b. = mass of water /mass of dry solid (bone dry)
w.b. = d.b./d.b.+1 ………. d.b.=w.b./1 – w.b.

12 Drying is a highly energy -intensive process, accounting for 10 –20% of total industrial energy use
in most developed countries. The main reason for this is the need to supply the latent heat of
evaporation to remove the water or other solvents. Effective analysis of current energy use is a
vital first step in identifying opportunities for savings.
q=KA [(T1 -T2)/X]

q :drying rate kW

K: thermal conductivity of the fuel,
A: is the surface area of the fuel particle
T1: is the temperature at the Surface of the particle (nominally 350F) (176C)
T2: is the temperature at the center of the particle
X: is the radius of the fuel particle.

Drying flowchart scheme [4]
ḿa =air mass flow kg dry air/ hour
ḿp = product flow kg dry product / hour
W =absolute humidity kg water /kg dry air
w =product moisture content dry base kg water / kg dry sold
Mass balance: ḿaW2+ ḿpw1 = ḿaW1+ ḿpw2
Energy balance: ḿaHa2+ ḿpHp1= ḿaHa1+ ḿpHp2+q losses
Ha= thermal energy of air kJ/kg dry air
Hp=thermal energy of product kJ/kg dry solid
Dryer ḿa,Ta1,W1
ḿp,Tp1,w1 ḿa,Ta2,W2
ḿp,Tp2,w2
Air
Product Energy lost q kw/h

13 Pyrolysis
Is the thermal decomposition of materials at elevated temperatures in an inert atmosphere? It
involves a change in chemical composition and is irreversible. The word is coined from the
Greek -derived elements pyro "fire" and lysis "separating“ The pyrolysis products are mainly tar
and carbonaceous charcoal, and low molecular weight gases. In addition, CO and CO2 can be
formed in considerable quantities, especially from oxygen -rich fuels, such as biomass. Fuel type,
temperature, pressure, heating rate and reaction time are all variables that affect the amounts and
properties of the products formed Pyrolysis is most commonly used in the treatment of organic
materials. It is one of the processes involved in charring wood. In general, pyrolysis of organic substan ces produces volatile products and leaves a solid residue enriched in carbon, char. Extreme
pyrolysis, which leaves mostly carbon as the residue, is called carbonization .
Pyrolysis generally consists of heating the material above its decomposition tempera ture,
breaking chemical bonds in its molecules. He fragments usually become smaller molecules but
may combine to produce residues with a larger molecular mass. T he starting material may be
heated in a vacuum or in an inert atmosphere to avoid adverse chemi cal reactions. Pyrolysis is a
vacuum also lowers the boiling point of the byproducts, improving their recovery.

Pyrolysis thermal scheme [5]

14 • Below about 100 °C, volatiles, including some water, evaporate. Heat -sensitive substances,
such as vitamin C and proteins, may partially change or decompose already at this stage.
• At about 100 °C or slightly higher, any remaining water that is merely absorbed in the
material is driven off. Water trapped in crystal structure of hydrates may come off at
somewhat higher temperatures. This process consumes a lot of energy, so the temperature
may stop rising until this stage is complete. [5]
• Some solid substances, like fats, waxes, and sugars, may melt and separate.
Between 100 and 500 °C, many common organic molecules break down. Most sugars start
decomposing at 160- 180 °C. Cellulose, a major component of wood, paper, and cotton fabrics,
decomposes at about 350 °C. Lignin, another major wood component, starts decomposing at
about 350 °C, but continues releasing volatile products up to 500 °C. The decomposition products
usually include water, carbon monoxide CO and/or carbon dioxide CO2, as well as a larg e
number of organic compounds. Gases and volatile products leave the sample, and some of them may condense again as smoke. Generally, this process also absorbs energy. Some volatiles may ignite and burn, creating a visible flame. The non -volatile residues typically become richer in –
carbon and form large disordered molecules, with colors ranging between brown and black. At this point the matter is said to have been "charred" or "carbonized .
• At 200- 300 °C, If Oxygen Has Not Been Excluded, The Carbonaceous Residue May Start To
Burn, In A Highly Exothermic Reaction, Often With No Or Little Visible Flame.
• Once Carbon Combustion Starts, The Temperature Rises Spontaneously, Turning The
Residue Into A Glowing Ember And Releasing Carbon Dioxide And /Or Monoxide.
• At This Stage, Some Of The Nitrogen Still Remaining In The Residue May Be Oxidized
Into Nitrogen Oxides Like NO2 And N2O3. Sulfur And Other Elements
Like Chlorine And Arsenic May Be Oxidized And Volatilized At This Stage. [5]
The decomposition products usually include water,
carbon monoxide CO, and/or carbon
dioxide CO2, as well as a large number of organic compounds . This Process Also Absorbs
Energy.

CaHbOc + heat → H20 + C02 + H2 + CO + CH4 + C2H6 + CH20 + . . . + tar + char

15 Gasification
Is a process that converts organic or fossil -based carbonaceous materials at high temperatures
(>700°C), without combustion, with a controlled amount of oxygen and/or steam into carbon
monoxide, hydrogen, and carbon dioxide. The feedstock is exposed to a high – temperature
atmosphere and hot particles, which heat the fuel leading to thermal decompositi on. In addition
and in contrast to pyrolysis, the material is brought into contact with a gasifying agent. At
reasonably high temperatures (ca. 800 –1400°C), reactions between the gasifying agent and the
solid carbon structure originating from the supplied feedstock take place, forming carbon oxides
or hydrocarbons (which are the main components of the product or producer gas).

Gasification Chemical Reactions
The transformation of solid fuel into gaseous substances by gasification takes place in hundreds
of reaction steps with dozens of intermediates. It is a very complex reaction network influenced
by feedstock properties, reactor design, gasifying agents, temperatures, residence times, and pressure .In general, the gasification reactions can be distinguished as gas -solid (heterogeneous)
reactions and gas –gas/gas –vapor (homogeneous) reactions. [6]
Reactions with Molecular Oxygen (Combustion React ions)
C + O2 = CO 2 Δ H = −110.62 kJ/mol
2 CO + O2 = 2 CO 2 Δ H = −283.15 kJ/mol
2 H 2 + O2 = 2 H 2 O Δ H = −242.00 kJ/mol
These combustion reactions are exothermic. The partial combustion of some of the feedstock and
some of the formed gases and vapors generates the heat needed for the endothermic conversion reactions. This is also how heat is supplied in auto thermal gasifier , where the required heat of
reaction is prod uced by partial oxidation within the gasifier
[30]

16 Reactions with Carbon Dioxide Boudouard Reaction:
C + CO2 = 2CO Δ H = +172.54 kJ/mol
Hydrocarbon/CO 2 reaction:
C n H m + n CO 2 = 2n CO + m/2 H 2
Carbon dioxide is used as a gasifying agent although much less frequently. Carbon dioxide is
formed by the thermal decomposition of oxygen containing biomass feedstock. The equilibrium
condition for the Boudouard reaction is strongly temperature dependent. With higher
temperatures, more CO will be formed.
Reactions with Steam
Heterogeneous water –gas reaction (although the ‘water’ is actually ‘steam’ in gasification
processes, ‘water’ is still used as a descriptive term in many gasification reactions):
C + H 2 O = CO + H 2 Δ H = +131.38 kJ/mol
Hydrocarbon/Steam Reaction:
C n H m + n H 2 O = n CO + (m/2 + n) H 2
Water gas – shift reaction (homogeneous water –gas reaction, shift conversion):
CO + H 2 O = CO 2 + H 2 Δ H = −41.16 kJ/mol
The heterogeneous water –gas reaction requires a heat supply and so is a reaction between
hydrocarbons and steam, which leads to the formation of hydrogen The water -gas- shift reaction
is an exothermic reaction and the heat released, although much smaller than the heat needed for
the heterogeneous water –gas reaction, is utilized within a gasification process.
Reactions with Hydrogen
Methanation (methane formation reaction, hydrogenating gasification, hydro gasification):
C + 2H 2 = CH 4 Δ H = −75.00 kJ/mol
The methane form ation reaction is a relatively slow reaction, which is favored at higher pressures.
It is under examination for the generation of SNG” Synthesis gas, or more commonly syngas, is a
mixture of carbon monoxide (CO) and hydrogen (H 2) and it is used in catalyz ed gas synthesis
reactions . Since the product gas produced by gasification using oxygen and/or steam as the
gasifying agent contains large amounts of CO and H2, the product gas is often called syngas.
The H 2 /CO ratio is given as required for the individ ual reaction.

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Complete Combustion

Includes the processes of pyrolysis and gasification and results in high temperature (>1400°c)
oxidation of biomass. The resulting flame oxidizes volatile gasses to carbon dioxide and water vapor
while the biomass is turned to ash. Ash is the non- carbon compounds found in biomass, such as
phosphorous and oxides of potassium, calcium, magnesium, sodium, iron and manganese.
[30]

18

PAhs ; Polycyclic aromatic hydrocarbons are primarily found in natural sources such as creosote.
They can result from the incomplete combustion of organic matter. PAHs can also be produ ced
geologically when organic sediments are chemically transformed into fossil fuels such as oil and
coal
HCs are emitted from exhausts as unburnt fuel and also through evaporation from the fuel tank,
from the nozzle when you fill up and also at stages th rough the fuel supply chain. They react with
NOx in sunlight to produce photochemical oxidants (including ozone), which cause breathing problems and increased symptoms in those with asthma.

Overall Schematic of Solid Fuel Combustion [31]

19 Review for research subject

Nguyen, et al [8] worked on Oxy-combustion with a circulating fluidized bed (Oxy -CFBC) can
facilitate the separation of high CO2 concentration and reduce emissions by biomass co -firing. It was
noted that: with increasing input oxygen levels (21–29 volume %), and biomass co -firing ratios (50,
70, and 100 wt% with domestic wood pellet). The possibility of bio -energy carbon capture and
storage for negative CO2 emission was also eval uated us ing a 0.1 MWth Oxy -CFBC test-rig. The
results show that combustion stably achieved with at least 90 vol% CO2 in the flue gas. Compared to
air-firing, oxy -firing (with 24 vol% oxygen) reduced pollutant emissions to 29.4% NO, 31.9%
SO 2 and 18.5% CO. Increas ing the biomass co -firing from 50 to 100 wt% decreased the NO, SO 2 and
CO content from 19.2 mg/MJ to 16.1 mg/MJ, 92.8 mg/MJ to 25.0 mg/MJ, and 7.5 mg/MJ to
5.5 mg/MJ, respectively. In contrast to blends of sub -bituminous coal and lignite, negative
CO 2 emis sion (approximately −647 g/kW th) was predicted for oxy -combustion only biomass.
Farooq , et al [9] worked on t hree biomass fuels, one woody and two non -woody have been tested in
a 20 kWth fluidized bed combustor. The effect of combustion atmosphere (air or oxy -fuel) and
oxygen concentration in the oxidant under the oxy -fuel combustion conditions on temperature
profiles and gas emissions (NOx and CO) were systematically investigated. The following
conclusions can be drawn from the obtained experimental results: a)Replacing the air with an oxy –
fuel oxidant comprised of 21 vol% O2 and 79 vol% CO2 results in a significant decrease in gas
temperatures and ulti mately leads to the extinction of the biomass flame due to the larger specific
heat of CO2 compared to N2. To keep a similar temperature profile to that achieved under the air
combustion conditions, the oxygen concentration in the oxy -fuel oxidant of O 2/CO 2 mixture has to be
increased to ca. 30 vol%. B) A drastic decrease in CO emissions can be achieved for all three biomass
fuels (up to 80% reduction when firing straw) under oxy -fuel conditions when the oxygen
concentration in the oxy- fuel oxidant is 25 vo l% or more as a result of the higher residence time of
the gas inside the combustor and the freeboard/reactor temperature profile matching that of air
combustion .C ) NOx emissions decrease with the oxygen concentration in the oxy- fuel oxidant due to
i) the increase of bed temperature, which implies more volatile- N released and converted in the dense
bed zone that contains many fuel -rich pockets and ii) the less dilution of the gases inside the dense
bed zone, which leads to a higher CO concentration in this region enhancing the reduction of NOx.
Similar NOx emissions to those obtained with air combustion were found when the biomass
Ali shah, et al [ 10] worked on the behavioral changes in fuel inherent nitrogen during combustion and
its distribution between elemental nitrogen (N2) or nitrogen oxides (NOx) after the combustion.
Nitrogen distribution between NOx and N2 has been evaluated for biomass combustion. A) Chang e
in oxidizer atmospheres from air to O2/CO2 enha nces nitrogen fixation rate. B) Relative increment in
O2 over partnering CO2 in oxy -combustion boosts NOx reduction. C) CO profiles influence nitrogen
behavior approaching to drop in NOx emissions. D) Around 80% reduction in NOx emissions under

20 oxy biomass combustion has been achieved. It was concluded that oxygen played a key role in
achieving a satisfactory reduction in NOx emissions
Kayahan , et al [11] studied o xygen enriched combustion a promising retrofitting option for existing
power plants to improve CO2 capture. In this study, the effect of oxygen enrichment of air as oxidant
was investigated with a 30kWth fluidized bed combustor. Tests were conducted with two different
Turkish lignite s, one biomass and their blends. Biomass share was increased up to 20%. The oxygen
concentration in the oxidant was kept between 21 and 30%. Oxygen enrichment supports combustion
in all cases. Biomass addition to lignite’s appears to have an increasing synergetic effect on
combustion as the oxygen enrichment and biomass portion in the mix increases. It was found that oxygen enrichment increas es NO and SO2 formation in all cases. As
the biomass share increases NO
emissions increase in all oxygen cases while the opposite is true for SO2 emissions.
Luo.et al [12] worked on the oxygen -enriched combustion of biomass micro fuel (BMF) was carried
out respectively in the thermogravimetric analyzer and cyclone furnace to evaluate the effects of oxygen concentration on combustion performance. The experimental results show that with the increasing oxyg en concentration, the volatile releasing temperature, ignition temperature and burnout
temperature were decreasing. Oxygen -enriched atmosphere subtracts burning time and improves
combustion activity of biomass micro fuel. Oxygen -enriched atmosphere improve s the combustion
temperature of BMF in cyclone furnace; while the improvement is weaken as oxygen concentration is
above 40%.
Engine. et al [13
] worked on the comparative combustion processes of two lignit es in the air, the
oxygen -enriched air , and the oxy -fuel environments. Combustion experiments were conducted in a 30
kWth circulating fluidized bed (CFB) combustor. The air combustion and the oxygen- enriched air
combustion were conducted with different excess air ratios and excess oxygen percentages,
respectively. Emissions of major pollutants such as CO, CO2, NOx and SO2 were measured during experiments via on -line gas analysis systems. Similarly, temperatures along the combustor axis were
measured at v arious positions. The oxy -fuel combustion experiments were done with O2/ RFG (O2/
recycled flue gas), mixture . In all environments, the lignite sustained stable and steady combustion
processes in the temperature range of 700 –950 °C under the conditions appl ied. Emissions of both
NOx and SO2 appeared to be considerably affected by combustion atmospheres. In the oxygen –
enriched combustion both the NOx and SO2 emissions were higher than that in the air combustion and increased with increase in the O2 concentrat ion in the feed gas. In comparison to the air and the
oxygen -enriched air combustion processes, however,
the NOx emissions were considerably depressed
in the oxy -fuel combustion . In the oxy- fuel combustion processes, CO2 concentrations of up to 96%
in the flue gases were reached on a dry basis.
Riaza.et al [14] worked on t he combustion behaviors of four different pulverized biomasses were
evaluated in the laboratory. Single particles of sugarcane bagasse, pine sawdust, terrified pine sawdust and olive residue were burned in a drop -tube furnace, set at 1400 K, in both air and O 2/CO2

21 atmospheres containing 21, 30, 35, and 50% oxygen mole fractions . Combustion of these particles
took place in two phases. Initially, volatiles evolved and burned in spherical envelope flames of low –
luminosity; then, upon extinction of these flames, c har residues ignited and burned in brief periods of
time. This behavior was shared by all four biomasses of this study, and only small differences among
them were evident based on their origin, type and pre -treatment. Volatile flames of biomass particles
were much less sooty than those of previously burned coal particles of analogous size and char
combustion durations were briefer . Replacing the background N2 gas with CO2, i.e., changing from
air to an oxy -fuel atmosphere, at 21% O2 impaired the intensity o f combustion ; reduced the
combustion temperatures and lengthened the burnout times of the biomass particles . Increasing the
oxygen mole fraction in CO2 to 28e35% restored the combustion intensity of the single biomass
particles to that in air.
Galina et a l [15] this experiment aims to characterize the thermal behavior of mixtures of coal,
sugarcane bagasse, and biomass sorghum bagasse as biomass in simulated combustion (O2/N2) and
oxy-fuel combustion (O 2/CO2) environments. Experiments have been performed in duplicate on a
thermogravimetric analyzer at a heating rate of 10 °C/min. A uniform granulometry was considered for all materials (63 μm) in order to ensure a homogeneous mixture. Four biomass percent ages in the
mixture (10, 25, 50 and 75%) have been studied. Based on thermogravimetric (TG) and thermogravimetric (DTG) analyses, parameters such as combustion index, synergism, and activation energy have been determined, as well as the combustion environm ent influence on these parameters.
The results indicate that, although sugarcane bagasse has the lowest activation energy, the thermal
behavior of both types of biomass is similar. Thus, biomass sorghum bagasse can be used as
alternative biomass to supply the power required during sugarcane off -season.
For both mixtures,
optimal results were obtained at 25% of the biomass . By analyzing the environment influence on
combustion behavior, the results indicate that when N2 is replaced with CO2, it is observed an
increase in reaction reactivity , a higher oxidation rate of materials and an improvement in evaluated
parameters.
Zayoud et al [ 16] noticed that . In fluidized beds and pulverized unites, enhanced heat t ransfer and
recirculation flue gas are used. On the other hand, higher oxygen concentration has pluses viz. better heat transfer, higher efficiency, compact setup and lower installation and operating costs. In pulverized power unites, pure oxy -fuel combust ion is used with 100% O
2 in the oxidant. In contrast,
the highest experimental O 2 % in oxy -fuel circulating fluidized bed (CFB) combustor is 70%. To the
best of authors’ knowledge, there is no single CFB power plant operating under pure oxygen condition… In this work, we are aiming to use pure oxygen for oxy -CFB combustion, with
new
temperature controlling method for CFBs depending on combustion staging by fuel staging rather
than using RFG . Fuel staging allows controlling combustion and varying SR. At the first stage, the
used oxidant is 100% O 2, and fuel is fed to achieve over SR (λ>1 ), where the excess oxidant absorbs
heat and does not take a part in the reaction . The products of the first stage are reaching of O 2 and
subsequently it is used as an oxidant for the second stage. For validation, a series of experiments are conducted usin g mini- CFB, and an oxidant of 100% O2 concentration is used with three SR ratios

22 λ=1.25, 2.0, and 3.0. The resulted average temperatures along the riser for biomass are 1031°C,
950°C, and 798°C; and for coal 1129 °C, 1051 °C, and 961 °C respectively. The controlling of AFT
with pure oxy -fuel combustion eliminates the recycled flue gas (RFG) in oxy -fuel CFB combustion
and flue gas recirculation section; this simplifies the power plants’ design, fabrication and its
installing -operating costs. Familiarizing this concept can accelerate adapting oxy -fuel combustion in
CFB power plant for Carbon Capturing and Sequestration (CCS). This contribution can commence
and commercialize the third generation of oxy -fuel CFB combustion with zero recycled flue gas .
Finally, t he concept of controlling AFT by SR (λ) is validated experimentally .
In Shi et al [ 17] experiment, supercritical oxy -fuel combustion system based on CFB boiler firing
coal, lignite and sawdust is established to evaluate the system performance. Five primary units are arranged including an air separation unit, a CFB combustor considering the fuel combustion
characteristics, a steam generation cycle, a simplified power island and CO2 purification and compression unit. After the validation, the influence of fuel types, oxygen concentration, flue gas recirculation forms and exhaust flue gas temperature on the system performance including adiabatic flame temperature, flue gas loss, net efficiency and exergy efficiency are evaluated. The results showed that compared to lignite and sawdust combustion,
oxy-fuel combustion with coal has the
highest net efficiency and exergy efficiency which is mainly because of the lower moisture and ash .
However, the drying process will not significantly increase the net efficiency of sawdust combustion according to the electricity consumption of biomass drying. Also, a dry cycle is preferable in high moisture fuels combustion due to the better burnout performance and less recirculation fan work.
To
increase the net efficiency, reducing the exhaust flue gas temperature and increasing the combustion
pressure are both eff ective.
Kumar, et al [ 18] the Experimental results are obtained from the co -firing coal with biomass under
air-fired and oxygen -enriched conditions in a 20 kW bubbling fluidized bed (BFB). Coal -biomass
blends burned effectively under the oxygen- enriched bubbling fluidized bed, and the burnout of the
blend is improved with an increase in oxygen concentration. Temperature profiles along the height of combustor for three cases concentrated on are fairly unif orm under air -fired and oxygen -enriched
conditions. The maximum temperature is observed in the splash zone for both air -fired and oxygen-
enriched conditions.
A rise in temperature at a height of 1.4 m above the distributor plate is observed,
which demonstr ates significant burning of fuel in the freeboard. With the supply of additional
oxygen , a considerable increment in temperature all through the combustor is observed in all cases.
The impact of additional oxygen on the temperature profile is dominating because of the effective
burning of fuel in the splash zone. At the point when a steady state is reached the amount of the fuel supplied is stable, and the oxygen concentration is increased inside the combustor. With the rise in combustion rate
, the concen tration of CO reduces gradually, and NOx concentration increases the
permissible limit . PJ and PN show promising results when co -fired with coal under oxygen -enriched
conditions. A maximum possible combustion efficiency of 97.09% could be achieved with 75%coal/25%PJ under oxygen -enriched condition. The total exergy destruction rate (66.787 kJ/h) it
is maximum for a blend of 25%coal/75%PJ under the oxygen -enriched case. Exergy efficiency is

23 varying from 30% to 58% for all the cases. Maximum exergy efficiency 57.4 is reported for a fuel
blend of coal + PL + PN + RH in case- 2.
Zhou et al [ 19] studied the characteristics of biomass combustion in industrial -scale grate boiler under
different operating conditions are investigated based on the numerical model. On account of the one –
dimensional dynamics assumption, a fuel bed model is developed to simulate the biomass
incineration on the grate bed, while interacting with three- dimensional CFD furnace model to provide
a thoughtful representation of the whole boiler. The model validation is performed based on the
experimental data and is used as the standard basi s for further investigation. The effect of air supply
is analyzed with a combination of numerical results and efficiency analysis. Under constant excess air
ratio, the thermal efficiency of the boiler is raised greatly when the primary air supply is elevat ed to
43% of the total air supply, but the improvement is limited when the ratio of primary air is further increased to 50%. The influence of redistribution of primary air supply in zone 4 and zone 5 on the thermal efficiency is dependent on the conversion rate of fuel in the first three zones, although the
bottom ash temperature can be reduced through increasing the airflow in zone 5. An increase in excess air ratio contributes to better burnout but stack loss increase simultaneously, so an optimum ratio is found to be 1.6. Oxygen -enriched combustion is also explored in this study.
The combustion
improves obviously by enriching the volume fraction of O2 in primary air to 25%, and the highest
temperature in the grate bed is below 1400 K, which is the limitat ion from the design specification of
this commercial grate boiler.
Mureddu in el at [20] studied the results of air -blown combustion and oxy -combustion kinetic
characterization (comparing two different is conversional methods: "Flynn -Wall -Ozawa" and"
Kissinger -Akahira -Sunose" of different kinds of coal (from Italy, South Africa and Hungary) and
biomass (pine and eucalyptus chips) by thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC ) together with the assessment of different characteristic combustion parameters. It
can be observed that the burning rate of fuels can be improved by the oxy -combustion process,
shortening the burning time (a mean reduction of the burnout time of 14% and 22% can be observed for coal and biomass samples, respectively). Moreover, biomass shows better ignition performance
than coal and enhances combustibility indexes (S and Hf), especially in oxy- combustion conditions.
For example, the S index, which reflects combustion properties, increases by an order of magnitude
for biomass combustion and oxy -combustion with respect to coal values, thus indicating a higher
combustion activity for biomass; an opposite trend can be observed for the Hf index, which describes
the rate and intensity of the process and is lower for biomass than for coal, thus indicating better performance for wood chips combustion. Kinetic analysis shows that the activation energy Ea varies with conversion values, reflecting the kinetic complexit y in both the processes. Moreover, with the
same range of heating rates (10 ≤ β ≤ 50 °C/min) and for the overall range of conversion
(0.1 ≤ α ≤ 0.9), both of the models used fit the experimental data in combustion regime
, whereas the
increase of the oxygen concentration makes the results reliable for coal samples and more sensitive to
weight loss for biomass samples.

24 Yan el at [21] worked on a bench- scale spouted fluidized -bed reactor was used to investigate the
combustion kinetics of pulverized woody biomass under air and oxy -fuel atmospheres. Bed
temperatures were in the range of 923−1073 K and O2 concentrations were varied from 20−35 vol %.
The activation energies and ap parent orders of reaction were calculated for air and oxy -fuel
combustion by means of an nth order Arrhenius equation approach. Results indicated that the
apparent order of reaction for both air and oxy -fuel combustion was approximately zero. The
activatio n energies were calculated assuming a zero -order reaction mechanism and were averaged
over all oxygen concentrations for air and oxy- fuel combustion and found to be 18.95 kJ/mol and
26.93 kJ/mol, respectively. The rate of combustion under oxy -fuel conditio ns was, on average, 37.5%
higher compared to air combustion . The shrinking core model with a reaction -controlled step was
found to accurately represent the biomass combustion reactions under both air and oxy -fuel
conditions.
Wang el at [ 22]they said Oxy -MILD (Oxygen Moderate and Intense Low -Oxygen Dilution)
combustion is one of the most promising technologies for the mitigation of CO2 emissions from coal –
fired furnaces, benefiting from its good performance in flame -temperature controlling an d NOx
reduction. Under oxy -MILD mode, the combustion or co- firing of biomass (CO2- neutral) can achieve
“negative CO2 emissions”. In this paper, oxy -MILD biomass co -firing is numerically studied by CFD
modeling for the IFRF furnace NO.1, where Guasare coal and Olive waste are co -fired under air –
MILD and oxy -MILD conditions, respectively. The effects of biomass co -firing ratio (0 –30%, energy
basis) and atmosphere on the temperature and heat flux distribution, and NOx emissions are
discussed. The modeling resu lts show that under MILD combustion mode, both oxy -combustion and
biomass co -firing can generate a more moderate temperature distribution and lower NOx emissions
than air -combustion and coal combustion, respectively. When biomass co -firing ratio increases from
0% to 30%, under oxy -MILD combustion mode, the peak temperature linearly decreases by 28 K and
the NOx emissions decrease by 141 ppm ; while under air -MILD combustion mode, the peak
temperature increases by 15 K and the NOx emissions decrease by only 7 3 ppm. This modeling work
suggests that oxy -MILD biomass co -firing is a more promising technology to achieve “negative CO2
emissions” in coal combustion, with lower furnace temperatures as well as NOx emissions.
Sung el at [ 23]Oxy-fuel co -combustion of waste sludge and biomass with flue gas recirculation was
conducted to observe the combustion characteristics and enrichment of CO2 using a 30 kWth
circulating fluidized bed. The combustion reaction was accelerated and the ignition time was
shortened by increasing the blending ratio of wood pellets and oxygen mixing ratio. The best
combustion performance was observed at a 30% blended biomass ratio, with 23% oxygen mixing rate as oxy co -combustion with respect to heat recovery and en richment of CO2; this study included
experiments with ranges of 0 to 70% for the blending ratio and 21 to 30% for the oxygen mixing
ratio. With flue gas recirculation at 60%,
the oxy- fuel co -combustion of sludge with biomass was
optimized in high enrichmen t of CO2 (over 90%) with less pollutant emissions, specifically 0.91%
CO and 14 ppm NO .

25 Tanui el at [ 24] This paper presents an investigation of wood combustion in a laboratory -scale fixed
bed with the ai m of establishing the effect of CO2 environment on flame propagation speed and
flame structures. Different oxy -fuel combustion atmospheres in which the composition of O2 in CO2
was varied from 21% to 50% by volume were tested and compared to air -fuel condi tion. Euler –
Lagrange (Computational Fluid Dynamics – Discrete Element Method, CFD -DEM) approach which
captures information of individual particle processes is used to model wood conversion in a packed
bed. Results show that flame front propagation speed in the oxy -fuel atmosphere reduced to 78% of
that of the air -fuel condition with similar O2 concentration. For oxy -fuel conditions, propagation
speed increased with increase in O2 concentration . The CFD -DEM model agrees very well with
experimental values for mass loss, propagation speed and flame front positions. However, peak
temperatures are poorly predicted at lower oxygen concentrations. The accuracy of temperature prediction improves at higher oxygen concentrations. During initial and devolatilization st age, mass
fraction of tar predicted in CO2 environment are smaller than in N2 environment, while the amount
of CO predicted is almost equal in both environments. However, during char combustion stage a high
amount of CO is observed in oxy -fuel conditions.
Moron el at [ 25] worked on the Co-firing biomass and coal under oxy -fuel combustion holds the
potential for negative CO2 emission into the atmosphere and is a promising technology to realized
atmospheric CO2 reduction and NOx and SO2 emission. NOx and SO2 emission and control is a
relevant element of combustion of fossil fuels and subject to strict supervision and monitoring. The implementation of combustion techniques in the oxygen -enriched atmosphere mak es it necessary to
get to know the oxy atmosphere, its impact and changes of combustion conditions onto the process of emissions of gaseous pollutants. NOx and SO2 emissions have been investigated for a different atmosphere in Entrained Flow Reactor. Exper iments co -firing hard and brown coals, wood and straw
pellets, and selected mixtures of these under three different atmospheres: air, oxy with recirculation
of dry and wet exhaust gases. The reactor set point temperature was held constant at 1000 °C, NOx
and SO2 emission levels were measured as a function of air excess ratio. The effect of fuel mixing,
fuel nitrogen and fuel sulphur content on the conversion of fuel nitrogen to NOx and fuel sulphur to
SO2 is also reported and discussed. The results obtained under oxy -fuel atmospheres were compared
with those attained in the air. The replacement of CO2 by 10% of steam in the oxy -fuel combustion
atmospheres was also evaluated in order to study the wet recirculation of flue gas.
The emissions of
NOx and SO2 dur ing oxy -fuel combustion were lower than under air -firing . Fuel mixing has a
positive influence on the NOx and SO2 emission level . Emissions of NOx and SO2 were significantly
reduced by the addition of biomass to the coal, but the addition of biomass can also increase the NO
emissions, it depends on the fuels nitrogen content .
Duan el at [ 26] Co-firing biomass and coal under oxy -fuel combustion in a circulating fluidized bed
combustor (CFBC) holds the pot ential for negative CO 2 emission into the atmosphere and is a
promising technology to realized atmospheric CO 2 reduction. Experiments co -firing coal and three
kinds of Chinese biomass, i.e. rice husk (RH), wood chips (WC) and dry wood flour (WF) under oxy –

26 fuel condition were carried out in a 10 kWt CFBC. Results show that burning biomass separately
produces higher NO emissions and a higher fuel nitrogen conversion ratio than burning coal without
biomass addition due to the higher volatile matter content of the biomass; the fuel nitrogen
conversion ratio is in agreement with the H/N ratio in the fuel under both air and oxy -fuel
atmosphere . In oxy -fuel combustion, lower NO emission is observed than in air combustion, because
CO 2 replacing N 2 reduces the yield of NO precursors like NH 3 during the devolatilization process
and enhances NO reduction via char/NO/CO reaction . NO emission increases as temperature, overall
oxygen concentration and primary oxidant fraction increase during oxy -fuel combustion. Oxygen
staging succeeds in controlling NO emission in a comparatively low level at high overall oxygen
concentration condition. The results can be helpful for the design and operation of the oxy -fuel
fluidized bed combustor.

Chansa el at [ 27] worked on the, thermogravimetric analysis (TGA) method has been used to evaluate
the kinetic behavior of biomass, coal and its blends during oxyfuel co -combustion. The
thermogravimetric results have been evaluated by the Coats –Red fern method and validated by
Criado’s method. TG and DTG curves indicate that as the oxygen concentration increases the ignition
and burn out temperatures approach a lower temperature region. The combustion characteristic index shows that biomass to c oals blends of 28% and 40% respectively can achieve enhanced combustion
up to 60% oxygen enrichment. In the devolatilization region, the activation energies for coal and blends reduce while in the char oxidation region, they increase with the rise in oxyge n concentration.
Biomass, however, indicates slightly different combustion characteristic of being degraded in a single
step and its activation energies increase with the rise in oxygen concentration . It is demonstrated in
this work that oxygen enrichment has more positive combustion effect on coal than biomass. At 20% oxygen enrichment, 28% and 40% blends indicate activation energy of 132.8 and 125.5 kJ/mol
respectively which are lower than coal at 148.1 kJ/mol but higher than biomass at 81.5 kJ/mol
demons trating the synergistic effect of fuel blending. Also, at char combustion step, an increase in
activation energy for 28% blend is found to be 0.36 kJ/mol per rising in oxygen concentration which
is higher than in 40% blend at 0.28 kJ/mol.
Huynh el at [ 28] worked on the investigate the characteristics of a biomass gasification system using
mixtures of “oxygen -enriched air” and steam as the gasifying agent for increasing the syngas heating
value and com bustible gas constituents . This study also aims to characterize the effects of oxygen –
and-steam gasification on ammonia concentration that can lead to significant NOx emissions from
syngas combustion. Experiments are conducted using a pilot -scale; pressuri zed bubbling fluidized
bed Gasifier with a capacity of five tons per day. Pure oxygen is added to air before mixing with
steam for gasification. A significant amount of steam is required to control the reactivity of the system at high oxygen levels. The ox ygen content in the enriched air varies from 21, 45, to 80 vol.%

27 on dry basis, corresponding to 21, 30, and 40 vol.% on wet basis respectively. The bed temperature is
maintained at 800 °C for all tests. Three different biomass feedstocks with nitrogen cont ents varying
from 0.05 to 1.4 wt% are used for study (i.e., pine, maple- oak mixture, and discarded seed corn). The
syngas dry composition is measured using a microgas chromatograph while ammonia concentration
and moisture content are measured using a modif ied IEA Tar Protocol and Karl Fischer Titration
respectively. Results indicate that oxygen -enriched air and steam gasification favors the production of
combustible gas components including hydrogen, carbon monoxide, methane, and lighter hydrocarbons
. When 40% oxygen is used, hydrogen increases by 70%, 47%, and 32% for pine,
maple -oak, and seed corn respectively, while CO increases by 34%, 18%, and 8.6% respectively.
Overall, it is found that oxygen and steam gasification is most effective for feedstock with low
nitrogen and moisture contents . Results also show that ammonia and NOx concentrations in syngas
increase as oxygen enrichment increases. The lower heating value of syngas can increase by as much
as 43% for the feedstock studied . When the oxygen level increases from 21% to 40%, the H 2/CO
ratio also increases from 0.59 to 0.75, 0.67 to 0.84, and 0.36 to 0.43 for pine, maple -oak, and seed
corn respectively . Despite the improvement, the H 2/CO ratio is still moderate. The moderate H 2/CO
ratio is explained b y the high water content in syngas at high oxygen and steam conditions, indicating
a large amount of un -reacted steam at the current gasifie temperature at 800 °C.
Pawlak el at [29] Experimental tests on co -firing of 20% straw -hard coal blend were conducted in
oxygen -enriched (up to 25 and 30%) atmospheres with three variants of O2 injection modes. NOx,
SO2 emissions and burnout for the various atmospheres in the combustion chamber w ere studied.
Moreover, co -firing tests were performed with a 40% share of wooden biomass to examine the effect
of the biomass share and a type on the emission of NOx and SO2 in OEA. The two O2 injection modes were investigated.
In each case, the emission of SO2 increases alongside an increase in
oxygen concentration in the atmosphere. However, the experimental results show that stable and
relatively low SO2 emission and low NOx emission can be achieved for OEA when oxygen is
supplied to the primary stream of air . Also, minimal LOI (loss on ignition) is obtained for OEA. The
supply of oxygen to the secondary oxidizer stream into the burner results in highest NOx emission only in the case of OEA30. It can be therefore concluded that both the oxygen -enriched a tmosphere
and the O2 injection mode affects NOx emission.

28 Conclusion

All research above mentioned that increasing the concentration of oxygen occur increases the
efficiency of combustion and reduce the CO2 and reduce the NOx and reduce the SOx And
some of the researchers got deferent results regarding the emission. Some of the researchers
have the opposite result there is no clear rule for the effect or standard base.
Only one thing Common to experiments it’s the oxygen concentration increase the e fficiency
and reduce some emission gases and increase other emission gases. This in itself leads to the benefit of "finding a mechanism to separate the flue gases elements by controlling the oxygen concentration".
In this experiment, I will be focusing on reducing the NOx, SOx and monitoring CO2 with
increasing the concentration of oxygen, affect of consenter the CO2 increase in flue gases, it’s
also to know the relationship that links the enhanced oxygen combustion with all elements which in flue gas emiss ion, Solid combustion residues and minerals to find an approximate
experimental relationship.
The enhancing of oxygen is a promising process in solid biomass combustion because of the high efficiency of oxyfuel combustion and Reducing CO2 using carbon capt ure & Storages
(CCS) technology. Also, the process of producing oxygen has become inexpensive.

29

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