Note: Descriptions are shown in the official language in which they were submitted.
~Z6!~55
The present invention relates to a method for
effectively utilizing waste rubbers, particularly waste
tires as fuel in apparatuses for burning cement.
Recently, the treatment of used waste tires has
become a great problem with development of automobile
industry. Waste tires have been partially directly used
effectively for fenders of ships and fish houses in sea but
the amount of utilization is very small. When waste tires
are subjected to burning treatment, public nuisance problems
of black smoke, unpleasant odor, NOx, SOx and the like must
be treated and the major part must be presently used for
the laying treatment.
The inventors have studied the effective uti-
lization of waste tires having heat energy of about 8,000
Kcal/kg and the method for treating a large amount of such
tires and the present invention has been accomplished.
The present invention comprises a method for
effectively utilizing waste tires in an apparatus for burning
cement using a rot:ary kiln, comprising the steps of feeding
waste tires directly without crushing or crushed waste tire
pieces as fuel to a position in the kiln where the gas tem-
perature in this apparatus is 600-1, 400C, said charging in
an amount not exceeding 60% of the total fuel use calculated
as heat energy.
It has been well known that in the production of
cement, combustible substances, such as spoil and the like
are charged in the apparatus for effectively utilizing the
generated heat in the steps for preheating and calcining
starting materials of cement or for solving the problem of
NOx, but the combustible substance in this case is powder.
While the size of waste tires charged in the present invention
~695S
is the waste tire as such or crushed waste tire pieces of
not less than 5 mm. The waste tire directly used without
crushing is not limited in the size, if the tire can be
charged into the rotary kiln In general, tires for passen--
ger cars, trucks, and buses are preferable. If waste tires
are crushed to a size of less than 5 mm, the particles
transfer mounting on gas flow and are burnt at the zone not
necessary heat and the temperature of the exhaust gas is
raised and the heat energy can not be efficiently used and
the fan sucking the exhaust gas is thermally damaged or
agglomeration occurs in a suspension preheater resulting in
clogging of cyclone and the stable operation for a long
period of time becomes difficult. The charging of an entire
waste tire as such is more preferable than that of crushed
waste tire pieces. Because, the finely crushed pieces are
burnt near the back of the kiln but in the case of waste
tire as such, the tire enters the inner portion of the ro-
tary kiln and the burning zone is elongated, so that the
reducing state advantageous for reducing the amount of NOx
can be kept along a long zone. But in the ca~e of the
crushed pieces, the finely divided powdery tire admixed,
so that there is fear that the stable operation for a long
time is damaged as mentioned above. If a consideration is
made in view of handling until charging, it is very difficult
to crush the waste tire into a given shape by means of the
presently known crusher and the crushed pieces are of an
irregular shape. Difficulties arise in the transferring
system until charging into the kiln because of the elastic
body, but in the case of the waste tire as such, the
transferring means presently generally used in tire factory
. .
:l~LZ69SS
advantageously can be directly utilized.
When the waste tires or crushed waste tire pieces
are charged into a zone where the temperature of the exhaust
gas is higher than 600C, they immediately start burning
and concurrently a part thereof is subjected to dry distilla-
tion owing to heating to generate reducing combustible subs-
tances. The combustible substances reduce and decompose
NOx generated from the main burner of the rotary kiln by
using the starting materials for cement as catalyst and the
burning of cement wherein the exhaust gas is low in NOx, can
be effected. When the waste tires or crushed waste tire
pieces are charged into a zone where the temperature of the
exhaust gas is lower than 600~C, if the crushed particles
are of a fine size, said particles are transferred to a
zone at a low temperature by the exhaust gas flow, and when
the particles are coarse, the particles stay at that position
and black smoke is generated due to the imcomplete combustion,
unpleasant odor is generated and NOx and SOx due to nitrogen
and sulfur contained in the waste tire itself are generated.
When the waste tire is charged toward a zone where
the temperature of the exhaust gas is higher than 1,400C,
for example the burning zone of the rotary kiln from the
front of the rotary kiln, a large cost is necessary for
obtaining finely divided powders. And in the case of gra-
nular or mass-shaped crushed pieces, the burning speed is
slow, so that it is difficult to maintain the temperature
of the burning zone. Particularly, in the case of mass-
shaped crushed pieces or tire as such, charging into the
burning zone becomes difficult. Accordingly, the position
for charging waste tires in the apparatus for burning cement
l~Z69SS
using a rotary kiln, as in the case of the rotary kiln alone,
the waste tires are charged into the preheating zone or the
calcining zone from the back or the side surface of the
rotary kiln. In the case of the burning apparatus provided
with cyclone system of preheater or calcining furnace, the
waste tires are charged into the position where the temper-
ature of the exhaust gas is higher than 600C in the accom-
panying installation for example the standing duct at the
back of the rotary kiln or the calcining furnace, in addition
to the above described positions.
The amount of waste tires or crushed waste tire
pieces charged is one which does not hinder the burning of
cement and is not more than 60% of the heat energy of the
whole fuel. When the said amount exceeds 60%, the stability
of temperature at the burning zone in the rotary kiln becomes
difficult and the quality of cement is adversely affected
and such an amount is not preferable. In general, a few
percent of zinc oxide (ZnO) i8 compounded in tire~ upon
the production as a vulcanization promoting assistant. It
has been reported in 5th Cement Chemistry International
Symposium Essay, Vol. 2, P. 444-453 that when more than
0.075% of ZnO is contained in cement, the setting of the
cement is retarded. According to experiments, when ZnO is
contained in an amount of more than 0.05%, the setting time
defined in JIS R5201 is not satisfied and further an amount
of unburnt carbon increases, so that the coating of the
preheater grows and the cyclone is clogged. Therefore, an
amount of waste tires or crushed waste tires charged is
preferred to be not more than 15%, more preferably 5-10%
of the heat energy of the whole fuel.
--5--
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112695S
When steel is contained in the waste tire, steel
is oxidized at the calcining zone and burning zone and
effectively acts as a part of the starting material of
cement.
The present invention has the following merits.
1. A large amount of waste tires can be treated.
2. Since waste tires are used as fuel, the heat energy of
the rubber itself can be effectively utilized.
3. A very large cost is needed for obtaining finely
divided tire powders but in the method of the present
invention the object can be attained by roughly crushed
pieces having a grain size of more than 5 mm, so that
the treatment for obtaining such crushed pieces is
simple.
4. The quality of the cement obtained is not adversely
affected
5. The secondary public nuisance due to burning of waste
tires does not occur. Rather, the amount of NOx
generated in the conventional burning of cement can
be reduced.
6. Waste tires can be used directly without crushing waste
tires, so that this method is advantageous inview of
noise of crushing and cost.
7. Waste tires including steel can be directly used in the
apparatus for burning cement.
The following examples are given for the purpose
of illustration of this invention and are not intended as
limitations thereof.
i~:
1~26955
Example 1
Waste tires were charged from the feeder of the
starting material provided at a back of a wet system of
rotary kiln having a diameter of 3,450 mm and a length of
66,300 mm and provided with a boiler. The obtained results
are shown in Table 1. The waste tires contained 20% of
steel.
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1~6955
When the size of the waste tires was not less than 50 mm and
the amount of the waste tire used was less than 60% of the
total used fuel calculated as heat energy, the amount of
heavy oil and NOx in the exhaust gas considerably decreased
as shown in Experiments 2, 3 and 4. On the other hand, when
the size was less than 1 mm, as shown in Experiment 5 the
amount of heavy oil used did not vary, the temperature of
the exhaust gas of the kiln was high and this case did not
act effectively as fuel, when the used amount is more than
60% of the total used uel calculated as heat energy, as
shown in Experiment 6 the temperature at the burning zone
was not stable and the burning was infeasible.
Example 2
Waste tires were charged from the upper portion
(gas temperature: about 1,000C) of the combined point of
the exhaust gas of the kiln and the gas discharged from the
cooler, said rotary kiln having a diameter of 5,250 mm and
a length of 84,1)00 mm and providcd wi-th a calcining Eurnace
and a suspension preheater. The obtalned results are shown
in Table 2. The waste tires contained 20% of steel.
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- 10 -
~6g55
When ~he size of the crushed waste tires was not
less than 10 mm and the amount of the waste tires was not
more than 60% of the total used fuel calculated as heat
energy, the amount of heavy oil used and NOx in the exhaust
gas considerably decreased as shown in Experiments 2, 3
and 4. On the other hand, when the size was less than 1 mm,
as shown in Experiment 5, the amount of heavy oil used did
not vary and the temperature of the exhaust gas has el.evated.
That is, i.n this casc, thc waste tires di.d not act
1(3 c:rfectively as fuel. Since the temperature of the exhaust
gas elcvated, it was impossible to more increase the
charging amount.
Example 3
~ shoot provided with air seal for crushed tire
pieces (size; 150-300 mm~ or tire (diameter: 770 mm,
breadth: 195 mm) was provided at si.de of shoot for starting
material entering four stages (lowest s-t~lge) o~ cyc:lone o:E
rotary kiln ~NS:P) hav:illg a d.iallleter Or 5,250 Illm and a length
of 84,000 mm and prov:ided with a calcining furnace and a
suspension preheater and crushed waste tire pieces or waste
tires were charged therein.
In addition, crushed waste tire pieces (size:
150-300 mm) were charged from a starting material feeder
providcd at the back of rotary kiln (WFB) having a diameter
of 3,450 mm and a length of 66,300 mm and provided with a
wct system of boiler into the kiln. In any case, the tire
contained 20% of steel and the heat energy of this tire was
7,500 kcal/kg, which corresponds to 77% of heat energy of
1 kg of heavy oil.
The obtained results are shown in Table 3,
- 11 -
~Z6g55
concerning the quality of cement, gypsum was added to the
obtained clinker so that S03 content in the cement becomes
2.2% and the mixture was crushed with a pot mill for
laboratory to obtain test cement and then the test cement
was evaluated by the mortar test of JIS R5201. The other
results were measured during operation.
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As seen from Table 3, when the amount of waste
tire charged increases, the setting time of the obtained
cement becomes longer and does not satisfy the cement quality
(starting time of setting: more than 1 hour, finishing time:
within 10 hours) defined in JIS. The coating growth of
preheater and clogging of cyclone owing to increase of
unburnt carbon occur frequently and the continuous safe
operation for a long period of time becomes difficult.
Accordingly, the amount of waste tires charged must be not
more than 15~ of thc total used fuel calculated as heat
energy and 5-10% is preferable taking the saving of the
amount of heavy oil into consideration. In comparison with
the use of crushed waste tire pieces, when the tire is
charged directly, the growth of coating of the preheater and
clogging of the cyclone do not substantially occur and the
temperature of the exhaust gas does not elevate.
Furthermore, the rotary kiln (SP) providcd wlth
suspension heater, whic}l is not prov:ided wlth the calcining
furnace showed the similar results to NSP.
- 14 -
