CHAP the gasification process: Thomas Shirley, 1669, performs

CHAP
1. RESEARCH BACKGROUND

Jan
Baptista Van Helmont, a Belgian chemist and physician, 1609, discovered that
gas could be produced from heating wood or coal and from this idea, several
others contributed in developing and refining the gasification process: Thomas
Shirley, 1669, performs various experiments with carbonated hydrogen. Robert
Gardner, 1788, became the first to obtain a patent dealing with gasification.
John Barber, 1791, received the first patent in which “producer gas”
was used to drive an internal combustion engine. Biomass gasification was first
conceived in 1798, when Philippe Lebon led efforts to gasify wood. The history
shows that gasification has grown from a simple conversion process used for
making “town gas” for industrial lighting to an advanced,
multi-product, carbon-based fuel technology of today and tomorrow. Gasification
was first used commercially in the 1800s for industrial and residential heating
and lighting. As the use and distribution infrastructures for electricity and
natural gas evolved, town gas use declined and gasification development paused.
However, history has shown that the technology is revisited when access to
natural gas, oil and petroleum products are limited through scarcity or high
prices. Today, gasification technology development is enjoying a renaissance as
a means for producing electrical energy, synthetic natural gas, liquid fuels or
chemical products from coal, biomass, or other carbon containing materials
under increasingly stringent environmental constraints. The gasification
process takes place in a device called a gasifier or gas producer, which can
range in size, shape, and design, depending on application or design year.

The
lack (or limit) of oxygen and slow burn rate causes the fuel in gasifier to
release flammable gases like methane, carbon monoxide, and hydrogen.
Nonflammable gases such as carbon dioxide and nitrogen are also released. The
syngas is then treated according to use. In short, gasification is defined as a
process of conversion of any solid or liquid carbon-based material (feedstock) into
gaseous fuel through its partial oxidation with air, oxygen, water vapor or
their mixture or as the thermo-chemical process limited to a partial combustion
and pyrolysis.

Gasification
is considered most suitable option of biomass energy conversion because of its
simplicity and economy viable to produce thermal energy or decentralized
electricity. The downdraft gasifiers are typically small-scale up to 5MW
capacity which facilitates their feasibility in remote areas such as villages
and islands. Modeling of this type of gasifier is about the design, predicting
operation behavior such as emissions during normal conditions, startup,
shutdown, change of fuel, change of loading, and to improve performance.

Downdraft
wood Gasifier requires wood chips, biomass briquettes or wood like
agro-residues (such as stems, stalks). Biomass gasification process usually
involves drying where moisture content is reduced up to 5% at 100-2000C,
pyrolysis where thermal decomposition of biomass occurs in the absence
of oxygen or air and volatile matter is released as a consequence of the
thermal break down of biomass. Here the mixture of gases carbon monoxide,
hydrogen, carbon dioxide and hydrocarbon gases from the biomass is released and
biomass is reduced to solid charcoal. The hydrocarbon gases condense at a low
temperature to generate liquid tars. Oxidation where solid carbonized
biomass is combined with oxygen in the air to form CO2 which lead to excessive
amount of heat release that is utilized for drying, pyrolysis and gasification
reactions. The oxidation of carbon and hydrogen also took place. Reduction during
which several endothermic reactions occur at 800-1000C such as Water–gas
reaction, boudouard reaction, shift reaction, methane reaction.

 

CHAP
2. RESEARCH PURPOSE AND SIGNIFICANCE

In
this research the modeling and optimization of a downdraft gasifier will be
conducted through mathematical model and simulation to save time and cost which
support preparation and optimization of experiments undertaken in real systems.
The simulations have to show comprehensive physical and chemical mechanisms
inside gasifier.to do so the combined transport and kinetic model will be
researched for efficiency improvement and optimization.

This
research will have great impact because it will help to deal with the climate
change which is a very problem that today’s world is facing. It will also my
impact my country energy because actually in my country we still have a problem
of energy where 45% of the population doesn’t have electricity or any other
energy from the grid. So the implementation of projects in this area will have
a big influence on my country energy generation as well I will acquire skills
to be involved in consultancy projects.

Biomass
gasifier is useful in different systems: driving of farm machinery like
tractors, harvesters; small scale electricity generation systems; irrigation
systems; direct heat systems (grain drying, green house heating and running of
absorption refrigeration and cooling systems, running of Stirling engines);
worked with other renewable energy systems like solar for thermal applications;
production of chemicals like Methanol and Formic acid; run a fuel cell plant.

CHAP 3. LITERATURE REVIEW

Downdraft
gasifier has worked on by different research and it is the most biomass energy
transformation interesting by its simplicity in design and implementation as it
can be used in remote areas. Einara Blanco Machin, at el. in their research Tar
reduction in downdraft biomass gasifier using a primary method, designed a 15
kW downdraft gasification reactor where the tar content obtained in the
experiments never overcome 10 mg/Nm3, with a lower heating value of 3.97
MJ/Nm3. some cool zones are created near to the nozzles, where the temperature
is not sufficiently higher to permit the thermal cracking of the tar present in
the mixture and to undergo its secondary gasification one of the tar presence
in producer gas.

Vimal
R. Patel at el. investigated the feasibility of the lignite as a fuel for
downdraft gasifier to evaluate the effect of the particle size on gasifier
performance and found that the increase in particle size results in the
reduction in fuel consumption rate with an increase in the producer gas
production rate. The heating value of the gas increases with particle size
increase from 13e16 mm to 22e25 mm and then same decreases with increase in
particle size. Higher temperature in reduction zone resulted in higher H2 and
CO contents in producer gas. Under the experiment conditions, the fuel
consumption rate, gas yields, LHV (Lower heating value) of gas fuel and cold
gas efficiency varied in the range of 9.58-10.67 kg/hr, 2.43-2.63 Nm3/kg, 3.33-
4.17 MJ/Nm3 and 51.5%-65.7% respectively. The experimental results showed that
the gasification performance was better with lignite particle size of 22-25 mm

I.-S.
Antonopoulos, at el. developed a non-stoichiometric model for a downdraft
gasifier was to simulate the overall gasification process where Mass and energy
balances of the gasifier were calculated and the composition of produced syngas
was predicted. The capacity of the modeled gasifier was assumed to be 0.5 MW,
with an Equivalence Ratio (EQ) of 0.45. The model incorporates the chemical
reactions and species involved, while it starts by selecting all species
containing C, H, and O, or any other dominant elements. Olive wood, miscanthus
and cardoon were tested in the formulated model for a temperature range of
800–1200 0C, in order to examine the syngas composition and the moisture impact
on the supplied fuel. Model results were then used in order to design an olive
wood gasification reactor.

Juan
Daniel Martínez, at el. In their review paper have studied the effects of the
particle size and the moisture content of biomass feedstock and the air/fuel
equivalence ratio used in the gasification process considering the quality of
the producer gas and its performance coupled with internal combustion engine:
downdraft gasification permits a higher conversion efficiencies with a low rate
of `tar due to gas passing through a high temperature zone (the combustion
zone), which enables the cracking of the tars formed during the gasification
process and particulate matter generation; the high char conversion and the
lower ash carry over since gases pass through the charcoal bed allowing its
filtration and catalysis and a quick response to any load change; it is
difficult to obtaining the homogeneous distribution of air in reactors with
large diameters which limits the gasifier capacity up to 5MW; downdraft
gasifier presents the potential difficulties with ash fusion and the necessity
to have feedstock with a moisture content less than 25%; the size of the fuel
particles (one-eighth of the reactor’s throat diameter is recommended) needs to
be adequate to sustain a certain biomass consumption rate (or a chemical
reaction rate), as well as to maintain an acceptable pressure drop inside the
reactor without the formation of preferential channels (bridging); A further
reduction of the tar concentration in the producer gas used in RICEs can be
achieved in downdraft gasifiers with a double stage air supply; equivalence
ratio and the superficial velocity are the critical design variable parameters
to ensure acceptable level of quality of the syngas. Equivalence ratio (ER)
range typically between 0.2 and 0.4, is the ratio of the actual air volume
supplied per kg of biomass fuel and the volume of air which is necessary for
stoichiometric combustion of the above amount of biomass fuel. Yamazaki et al.
reported a good performance gasifier with superficial velocity (SV) values of
about 0.4 Nm/s. SV, is a ratio of the syngas production rate at normal
conditions and the narrowest cross sectional area of the gasifier’. It has
shown that SV influences the gas production rate, the gas energy content, the
fuel consumption rate, the power output and char and tar production rates. It
is independent of reactor dimensions, allowing a direct comparison of gasifiers
with different power outputs. Low values of SV result in a relatively slow
pyrolysis process with high yields of char and significant quantities of
unburned tars. On the other hand, high values of SV cause a very fast pyrolysis
process, formation of a reduced amount of char and very hot gases in the
flaming zone. However, such high SV values may significantly decrease the gas
residence time in the gasifier, resulting in lower efficiencies in the tar
cracking processes. The main output parameters in the gasification process in
moving bed reactors are the producer gas composition, its calorific value which
depends mainly on the temperature in the reactor, which in its turn is
influenced by the ER value, thermal power of the gasifier, gas yield which is
directly proportional to the ER variation and to the residence time of the
gases in the reduction zone and the thermochemical process efficiency which
depends on the type of biomass used, its particle size, the ER value and the
reactor ‘design. Tinaut et al. used a two zone combustion model for the
description of the working process of an engine and concluded that the main
parameter defining the performance of the engine is the calorific value (per
unit volume) of the stoichiometric air/producer gas mixture. The above model
determines the fraction of the mass burnt the variation of the pressure and temperature
over the cycle and values of the engine’s efficiency and of its indicated mean
pressure. Using a parameter named as the Engine Fuel Quality (EFQ) the authors
estimated the magnitude of the power de-rating in the engine fuelled by the
producer gas.

Young-Il
Son,at el. studied on the characteristics of syngas production from biomass
gasification in a downdraft gasifier combined with a small gas engine system
for power generation. Syngas temperatures from the gasifier were maintained at
a level of 700-10000C. When the air ratio for gasification was 0.3-0.35, the
low heating value of syngas was 1100-1200 kcal Nm3 and the cold gas efficiency
69-72%. Tar concentration in raw syngas was around 3.9-4.4 g Nm3. Syngas
combustion in the gas engine after purification showed that HC concentration
was below 200 ppm, and NOx concentration was below 40 ppm in the exhaust gas.
It is generally known that the minimum calorific value required in the
application of syngas to a gas engine should be above 1000 kcal Nm3.

My
research is to investigation on modeling and optimization of the downdraft by
combined transport and kinetic model with the aim of efficiency improvement and
optimization with regard to the quality of syngas simulation results as well
tar reduction. Mathematical model and simulation will be carried out with
experiments to validate

CHAP
4. SCIENTIFIC PREPARATION OF THE APPLICANT

According
to the educational and professional background as shown in all the application
documents, I am mentally, physically and technically well prepared to
successfully achieve all the program related tasks within a specified period
with excellent outcomes.

CHAP
5. RESEARCH METHODS

The
research will be done using different methods such reading some literature
reviews to enrich the knowledge and skills in the field of biomass energy
especially design and optimization of different biomass energy conversion
methods. The mathematical models and simulations will be conducted using some
softwares that can be used in this fields such as matlab, CFD and others.
Experiments has to be done to validate the results