_________________________________________________________Introduction
such as the soaps formation (which wear the catalysts utilized) and their not
simple consequent removal from the final product.
All this with the purpose to minimize the energy cost and therefore to
maximize the plant’s global efficiency.
It is defined cogenerative a plant which, utilizing a determined type of
combustible, allows to produce electric and thermic power for different types of
users. Generally the cogenerative plants are installed inside industries which,
needing high needs of thermic power for their internal production processes,
combine such production with the one of electric power which can be partially
utilized for internal utilization and partially sold to the national network.
The cogeneration plant produces usually overheated steam or hot water
which can be utilized directly for the thermic users or transferred to intermediate
heat exchangers to heat the fluid to be utilized in the final thermic users.
For certain applications the air can be utilized as fluid vector which however
shows as main disadvantage low thermal exchange coefficients which compel to
adopt heat exchangers of large dimensions.
On the energy point of view, the cogenerative plant success is strongly
related to the electric and thermic production satisfying capacity, requested by the
users with combustible consumptions lower than those utilized in a separate
production of thermic and electric power in specific plants.
In the first chapter (“Biodiesel production”) it is mentioned the world’s
energy situation, presenting the biodiesel as a fuel able both to reduce the carbon
dioxide and other polluting components in the atmosphere, and to decrease the
energy dependence from the traditional fossil combustibles; afterwards are
described all the methods actually available for its production (acid, base,
enzymatic and in supercritical conditions catalysis). At last are handled all the
2
______________________________________________________Introduction
parameters influencing the different types of reaction and the specifications the
biodiesel must have in order to be marketed and therefore utilized in all the Diesel
cycle engines.
In the second chapter (“Cogeneration”) it is afforded in a deep manner the
cogeneration theme, greatly considered today, introducing all the evaluation
indexes and the reports useful for its handling. It is made a particular reference to
the cogenerative units by a steam turbine, because it is the resource to be
exploited in this Thesis treatise.
In the third chapter (“Biodiesel industrial production by basic catalysts”)
are listed the best technologies available for the transesterification of different
types of vegetable oils (sunflower, soya, colza, Brassica Carinata and palm)
combined with alcohol (methanol and ethanol) and catalyst (KOH and NaOH).
Are indicated in particular all the parameters involved, the diagrams and the
tables useful for the handling. The content of this chapter is the result coming
from various experimentations.
In the fourth chapter (“The existing steam and dealcoholization plant”) are
described the existing steam turbine alimented by vegetable biomasses, the marcs
dealcoholization system and all the accessory elements; are listed in particular the
function data concerning the electric power production, the combustible
consumptions and the smokes treatments.
In the fifth chapter (“Pure ethanol production”) are introduced simple and
fractional distillation concepts, focusing the attention on the problems due to the
physical ethanol-water azeotrope separation. It is then pointed to the azeotrope
elimination by benzene; at last it is deeply considered the saline-extractive
distillation by CaCI
2
, an innovative method which allows to obtain ethanol with
purity of 99.998% molar, always by the azeotrope elimination, and with minimum
energy dispersion, lower than different experimentations previously performed by
other authors.
3
_________________________________________________________Introduction
In the sixth chapter (“Biodiesel production plant scaling”), considering the
existing plant (steam turbine and dealcoholization system), the biodiesel
production plant is dimensioned, determining the raw material (vegetable oils,
ethanol, KOH catalyst), thermic and electric power amounts needed. In particular
the thermic power is exploited by tapping steam from the turbine while the
electric one is drawn by the alternator situated downstream the steam system.
Then it will be recalculated the turbine global efficiency performing a comparison
between the energy cost with cogeneration and the one related to the fossil
combustible.
In the Conclusions at last it is reassumed in large scale the entire work
performed, with particular consideration to the results obtained and to the present
project possible future developments.
_________________________________________________________________
4
___________________________________________Chapter1 – Biodiesel Production
1 - BIODIESEL PRODUCTION
1.1 General knowledge
The world’s energy problem is becoming of a vital importance for two
fundamental reasons, the natural resources reduction of fossil combustibles and
the atmospheric pollution.
These two aspects jointed don’t forecast anything good for the planet’s
future. From one side, the reduction of fossil combustibles supplies compels to
the research of new energy sources able to replace them; on the other side, the
climate variations now evident, supply a subsequent element to continue with
decision on this road.
The first effect is now evident at everybody’s eyes: in fact, the fossil
combustibles cost has reached such levels to put into discussion the life’s trend of
the Countries technologically advanced and to negatively weighs on the poor
Countries development.
A healthy energy policy should try to decrease these combustibles
consumptions in all those cases where are available possible alternatives, leaving
their utilization for all those sectors where it is impossible, at least for now, their
replacement with other energy sources; all this in order to considerably lengthen
the natural resources exhaustion date and at the same time to improve the
environmental conditions [10.]
5
___________________________________________Chapter1 – Biodiesel Production
The biodiesel can develop a more and more active role on the environmental
safeguard of our cities, because it is a low environmental impact energy source,
free of aromatic hydrocarbons such as the benzene, with lower particulates
emissions and sulphur-free. It is a renewable energy source and as such one of the
instruments individualized to restrict the carbon dioxide emission in atmosphere,
considered one of the gases most influencing the climate equilibrium of our
planet.
The biodiesel utilization crucial points are essentially two: the first one
concerns the quality intended as product’s specifications defined to grant the
correct running of the internal combustion engines actually in use and the second
one equally important is the biodiesel effective cost.
For what it concerns the first point it is sufficient to remember the recent
news regarding the utilization of colza oil in the cars and to explain as in reality it
isn’t true that if we introduce some oil in the engine this one doesn’t run; in
reality this one burns the oil which is always formed by hydrocarbons oxidating
themselves during the combustion but the problem is that on the long term the
engine will be ruined because of the oil density, of its viscosity (10-100 times
higher than those of the fissile diesel fuel, at the same temperature) and because
of the low cetane number, and this involves a higher fatigue mainly at the
engine’s ignition.
This point is fundamental in the reason why we cannot imagine to modify in
short times the technology of the engines utilized in order to adapt them to a
combustible formed totally of oil so that various methods are being developed in
order to make suitable for use this renewable resource.
Various solutions of the problem exist; the first one is to mix a percentage
of oil with the diesel fuel derived from crude oil in order to have a mixture with
characteristics closer to those usually utilized, the second one is to transform the
oil by a process defined “transesterification” into biodiesel, having well specified
6
___________________________________________Chapter1 – Biodiesel Production
parameters allowing it to be utilized as an excellent fuel for engines of this
generation, the other ones consist in the microemulsion with short chain alcohol
such as the methanol or the ethanol or in the pyrolysis or thermic cracking.
The most promising technique is the one of the “transesterification”. At this
point it enters into play the other fundamental knot that means the
transesterificated biodiesel cost: the final price depends much from the raw
materials utilized, therefore the development of this process is aimed to obtain a
product bearing the characteristics requested by the modern engines exploiting
raw materials having reasonable prices.
First of all it must be mentioned that the biodiesel’s lower production cost is
at least double than the one of diesel fuel or gasoline: however the only factor
which results to be highly incentivating is the environmental impact clearly lower
than the traditional combustibles one. In fact, it doesn’t contribute to the
«glasshouse effect» because it returns to the air only the amount of carbon
dioxide utilized by colza, soya and sunflower during their growth, it reduces the
carbon monoxide and hydrocarbons unburnt emissions, because it doesn’t contain
sulphur the Biodiesel doesn’t produce a highly polluting substance such as the
sulphur dioxide and allows catalytic mufflers higher efficiency, decreases in
comparison to diesel fuel the gases fumosity exhausted by the diesel engines and
by the heating systems (-70%), doesn’t contain very dangerous substances for the
health such as the aromatic hydrocarbons benzene, toluene, and homologouses or
polycyclic aromatics.
At this point it is necessary to mention the Kyoto protocol and the actual
situation in Italy for what it concerns the renewable combustibles and the
emissions.
The Kyoto protocol represents an important answer to reduce the CO
2
amounts released in atmosphere and to oppose the global climate changes. The
7
___________________________________________Chapter1 – Biodiesel Production
Protocol general targets are shared also by the Italian petrol industry. The
commitments undersigned in Kyoto by the industrialized countries forecast the
achievement of the glasshouse gases emissions reduction within the year 2010
compared to the year 1990 in the following value: European Union –8%; United
States –7%; Japan –6%. Italy assumed the commitment to reduce the glasshouse
gases emissions of 6.5% within the year 2010 compared to the year 1990
emissions. With the Kyoto Protocol ratification by the Italian Parliament, through
the Law n. 120 dated June 1
st
. 2002, Italy committed herself officially to respect
the obligations to reduce the glasshouse gases forecasted by the Protocol for our
Country. The necessary cuttings are estimated in 93 millions tonnes of CO
2
forecasted to be reached through three intervention’s sectors:
● activation of the energy industry’s containment measures;
● interventions in the agricultural and forestry sector;
● further measures in the civil and tertiary transports sectors;
● country modernization through the infrastructures achievement;
● achievement of new combined cycle plants and of new import lines from
abroad for gas and electricity;
● integrated management of the territory and environment for the
renewable energies exploitation particularly of the eolian one, the waste
handling and the biomasses exploitation.
On the environmental side it is estimated that the utilization of one kilogram
of biodiesel in replacement of the diesel fuel involves, in the best case, a
maximum decrease of CO
2
emissions of 2.1 kg (60% less as regard to the diesel
fuel emission which amounts to 3.2 kg of CO
2
).
On the fiscal point of view, in order to make the biodiesel competitive on the
market, it results necessary to exempt it completely from the excises. This last
aspect should make particularly onerous for the State budget the Resolution target
to increase the consumptions, in the transports sector, from the actual 250,000
tonnes to over one million tonnes within the year 2010.
8
___________________________________________Chapter1 – Biodiesel Production
1.2 Reaction and production
The refined oils aren’t suitable to be utilized exactly like, especially in the
Diesel engines, due to their high viscosity (70-80 cSt versus the 5-7 cSt of the
diesel fuel at 20°C). A clear improvement of this characteristic can be obtained
by the transesterification process which, as it can be observed in fig. 1.1, bears
as a more evident result the triglyceride’s molecule breaking into three smaller
molecules and therefore less viscous. .
Figure 1.1: methanolysis of a triglyceride.
As it can be observed the transesterification reaction, from a chemical point
of view, is very simple. One difficulty, on the contrary, is due to the fact that the
refined oil is formed by a mixture where the vegetable fats are present both under
shape of triglycerides and monoglycerides: the reaction therefore must be
optimized on the average of these compounds characteristics.
In order to obtain an ester it is needed to process the refined oil by an
alcohol (methylic, in almost the totality of cases, also if various tests have been
performed by ethyl alcohol) and suitable catalytics (normally alkaline like the
potassium hydroxide, sodium hydroxide or sodium methylate) which increase the
reaction’s speed and efficiency which in this way can occur at non high
9
___________________________________________Chapter1 – Biodiesel Production
temperatures and pressures. Otherwise it will be involved very long times or
temperatures in the amount of 250° C. For crude oils with high acidity (higher
than 1%) the utilization of alkaline catalysts can bear to the soaps formation , so it
should be better to utilize those acid ones. Normally however the refined oils have
a low acidity and therefore are utilized precisely alkaline catalysts. The final
product has a very lower viscosity (about 6-7 cSt at 20° C, of the same value of
the one of the diesel fuel) in comparison to the crude oil, the characteristics at
cold temperature are such to make it suitable for almost all the climates, the
cetane number increases of 12-15 units and in addition it is possible to add
mineral combustible in any proportion.
It is also obtained a by-product: an aqueous phase at glycerol base, whose
refining requests rather complicated installations. The simplified mass balance of
the entire process is the following:
1000 kg of refined oil + 100 kg methanol = 1000 kg biodiesel + 100 kg glycerol
Because of the tendency to obtain an high conversion rate into methyl ester (if
possible higher than 97%), it is needed to eliminate phospholipids and mucillages
and to maintain the oil’s acidity rate the lowest possible.
The process speed up is performed in two ways:
1. By adding methanol/ethanol in excess (typically in 1:6 ratio).
2. Elimination of the glycerine formed.
The methanol isn’t totally oil-soluble at ambient temperature, so it is needed
to have recourse to the mixture heating and stirring. The reaction temperature, in
effect, isn’t standard, but it must be individualized taking care also of the reaction
times. Indicatively after one hour aren’t observed significant yield differences at
temperatures of 45° C or of 60° C, while at 32° C the yield is slightly lower. On
the contrary after four hours the yield is around 98-99%.
10
Ricevi informazioni sui nostri servizi, sulle offerte e non perdere news e consigli su università e lavoro.
