Note: Descriptions are shown in the official language in which they were submitted.
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Tht? i.nventi.on relatcs to a pr~cess ~or ~repar.in~
a suC~ension o~ coal par~icles in a hydrocarbon ~uel. .
Such suspensions make excellent fuels and - i.f the suspended
: coal particles are small enough - can be atomized as
5a liquid fuel in a burner. For the preparation of the
suspensions the amount and particle size di.stribution
of the solid must be chosen such that a dynamically
and, if desired, statically stable suspension is obtained
. wherein the particles do not segregate or agglomerate.
10 The ultimately allowable viscosity, too, puts limits
to the amount and shape of the solid materi.al in these :~
suspensions, Within the scope of these limits it iS9
however very well possible to prepare attractive fuels.
As will Oe obvious the solid material, has to be
1~ distrlbuted as homogeneously as possible through the
. hydrocarbon fuel. With the preparation of the suspensions
the latter requirement gives rise to problems. It is .
difficult to mix an amount of dry coal powder homogeneously ~;
with the required amount of hydrocarbon fuel. Thls calls
for a relatively large amount of energy and expensive
apparatuses, one problem being the abrasive character
of dry coal powder.
For applicati.on of the suspensions as fuel it is
desirable that the coal particles contain as little ash
as possible. Since most coals contain a relatively high
percentage of ash, the coal often has to be de-ashed
before it can be made into the suspension. This de-ashing,
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too, requires relat:ively much energy and expensive aPparatuses.
The present invention aims at a combination o~ these
two at first sight not relate~ treatments and thus at
a considerably saving.
The suspension of coal particles in a hydrocarbon
fuel therefore i5 prepared, according to the invention,
by treating an aqueous suspension of ash-containing
; coal particles under turbulent conditions in an agglomeration
device with a hydrocarbon--based binder, resultin~ in
the formation of agglomerates of coal particles and binder,
while excluding at leasl; part of the ash, and by separating
, the obtained agglomerates from an ash-containing water
phase and taking them up in a hydrocarbon fuel, the
agglomerates being disintegrated and the resulting coal
particles becoming suspended in the hydrocarbon fuel.
In this way th~ coal is at the same time de-ashed
and brought in a form wherein it is relatively easy to
take the coal up in an excess hydrocarbon fuel. Owing
to the presence of the binder in the agglomerates and
to the fact that the agglomerates are much larger than
` the individual coal particles, the mixing o~ the coal
(i.e. the agglomerates) with the hydrocarbon fuel proceeds
much more easily than if dry coal powder would have to
be mixed with the fuel. Possibly this is partly due to
the fact that the coal particles have already been wetted
with hydrocarbon before the mixing with fuel takes place,
i.e. during agglomeration.
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The method accordin~ to t;he inve~tion starts from
an aqueous suspension of coal particles. This suspension,
whereof the percentage solids is not critical for the
agglomeration step, can, for example, be a pi~eline slurry.
The aqueous suspension may have been obtained by grin~ing
coal lumps wet, i.e. in the presence of water and - i~
desired - by mixing the obtained mass o~ ground coal
with an extra amount of water. Wet grinding of coal lumps
has some advantages over dry grinding; less energy is
required, dust problems are eliminated and there is no
explosion danger.
According to the invention the process starts from
an aqueous suspension of ash-containing coal particles.
In this specification this is meant to denote an aqueous
suspension of particles that consist mainly of coal.
In this context it is then possible that the suspension
contains coal particles which contain ash and/or that
the suspension contains ash particles besides the coal
particles. To a certain extent this depends on the history
of the coal and the suspension ln question.
As mentioned, the suspension is to be treated under
turbulent conditions in an agglomeration device with
a hydrocarbon-based binder. By contacting the suspension
at normal or elevated temperature with a suitable binder
and bylstirring vigorously, agglomerates are formed
of coal particles and binder. The binder should be of
the type that is capable of causing coal particles to
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stick together, to the extent that the particles are
wetted with the binder, are rendered hydrophoblc and
stick together. The ash particles that are set free durin~
the stirring, however, do not have such affinity for
the binder and are to a great extent not taken up in
the agglomerates. Due to the hydrophobic character of
the agglomerates it is relatively simple to separate
them from the water phase, which separation could for
example be effected by passing the stream of agglomera~e-con-
; 10 taining water, which originates from the agglome~ation
device, over a sieve on which the agglomerates stay
behind. Also, it is possible for example, to add in a
separate mixing device an amount of hydrocarbons to
the agglomerate-containing water phase, so that two phases
are present in this mixing device and the agglomerates
migrate from the water phase into the hydrocarbon phase.
The agglomerates can then be transported while suspended
in hydrocarbon. In all these cases the ash-containing
water phase may be separately withdrawn and processed.
The agglomerates are to be taken up in a hydrocarbon
fuel. This can be done during and/or after the separation
~fagglomerates and water phase. The agglomerates can,
after the said separation, for example, be mixed at once
` with the total amount of hydrocarbon fuel, which will
cost relatively little energy and whereby the agglomerateb
j can disintegrate and the mixture obtained being a homogeneous
suspension of coal particles in hydrocarbon fuel. It
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is also possible to mix the a~glomerates with part of
the total required amount Or hydrocarbon fuel as a result
of which a thick sludge is obtained which can subsequently
be diluted with the remainder of the hydrocarbon fuel.
; 5 The obtained suspension, if desired, can then be specially
homogenized~
After separation of the agglomerates from the water
phase, the agglomerates can suitably be distintegratedO
This can, for example, be done in a mill. It is possible
to distintegrate the agglomerates while they are as such.
It is preferred, however~ to distintegrate them while
they are already mixed with at least part of the total
required amount of hydrocarbon fuel.
For the process of the invention all sorts of coal
are in principle suitable, includin~ the solid fuels
that are related to coal, such as lignite, peat, bituminous
coal, soot, coke, etc.
The hydrocarbon fuel may be one of the usual liquid
fuels that are obtained from the processing of crude
oil. The fuels based on heavy oil fractions, such as
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fuel oil, lend themselves especially well for application
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in the present process.
As a binder for the agglomeration of the coal particles
` a permanent binder may be chosen, i.e. a binder which
is ultimately taken up in the fuel. It is also possible,
however, to choose a type of binder that is regained
from the agglomerates in the course of the process
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- of the invention and whi~h i~ then r~circulated. This
is posslble, for example, by using a light hydrocarbon
fraction as a binder and a heavy fraction as the fuel.
The agglomerates may then be mixed with the fuel at
a temperature above the boiling point or range o~ the
binder, whereby the binder can be regained.
Suitable binders are, in principle, all liquids,
or substances that are liquid at agglomerative conditions,
which are wholly or partly based on hydrocarbons, provided
10they have the other suitable properties This holds
for all kinds of products obtained from oil or coal,
such as naphtha, gas oil, fuel oil, bitumen, coal tar,
etc.
It is by all means possible, in principle, to use
the applied fuel also as a binder.
Depending on the concentration of solids in the
aqueous suspension, on the type of binder used and the
applied amount and on the flow conditions~ during stirrin~
varlous types of agglomerates may be obtained, ranging ~ ~;
from loosely bound, fluffy material to hard pellets.
It has been experienced that complete deashing or
deashing to the required degree may not always be reached
at once, especially in cases where a h;gh percentage
of ash is originally present in the coal. In this case
it is preferred according to the invention to mix the
obtained agglomerates after separation from the ash-containing
water phase with an additional amount of water and additional
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binder~ to disintegrate the agglomerate~ and to re-a~glomerate
the coal under turbulent conditions, whereafter the fresh
agglomerates are separated from the ash-containing water
and taken up in the hydrocarbon ~uel. Thus an additional / .
~ 5 deashin~ is obtained. The agglomerates can be disintegrated
before, during and/or after addition of extra water in
the first stage and addition of hydrocarhon fuel in the
second stage.
It has also been found disadvantageous to perform
the first agglomeration step of the above mentioned two
~ stage agglomeration process in a high shear agglomeration
; device in which, apart from the agglomeration itself,
the coal particles are further ground~ whereby even more
ash particles are liberated and thus separated. The obtained
s~spensions do have a superior long term stability.
The invention will be further elucidated by two
examples.
EXAMPLE I
; One kg of a coal slurry containing 200 gram of ash-containing
coal particles (all smaller than 500 ~, total ash content
56 %w) was agglomerated in a bench scale pelletizer (one
litre vessel; power input 10 Watt) with 20 gram of 800
sec.RI heavy fuel oil to small ( 1 mm) pellets. After
screening, the pellets retained on the sieve were found
to contain 25 %w of water and 18 %w ash on dry, hinder
free, basis. The wet pellets, approx. 150 grams, were
mixed with 100 gram of heavy fuel oil. The thus formed
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suspension remained stable for two hours. Thereafter
sett~ g started, whlch halted after approx. two days
when stlll approx. 80% of the coal was found to be in
suspenslon .
~XAMPLE II
; One kg of slurry as prepared in Example I was allowed
to settle until a virtually stable settled bed of coal
particles had been formed. The supernatant liquid and
the top half of the settled bed were set aside. The bottom
part containing the majority of the particles over 100
um were resuspended in water and agglomerated and ground
` in a high shear pelletizer (one litre vesselg power input
; 300 Watt) during one minute with 4 %w of heavy fuel oil
to form agglomerates. The coal particles in the agglomerates
were all passing a 200 ~m sieve and contained 8 %w of
ash. Then the agglomerates were resuspended in the remaining
portion of above slurry and further agglomerated with
in total 20 grams of binder.
The resulting pellets, 4 to 6 mm in size, contained
4 %w of water and 90 %w of ash on a dry and binder-free
basis. These pellets, approx. 120 grams, were mixed with
100 grams of heavy fuel oil to produce a non-settling
(two days' observation) suspension o~ coal in oil.
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