GB2034014A

GB2034014A - Method of utilizing waste tires

Info

Publication number: GB2034014A
Application number: GB7936196A
Authority: GB
Original assignee: Bridgestone Corp
Current assignee: Bridgestone Corp
Priority date: 1978-10-18
Filing date: 1979-10-18
Publication date: 1980-05-29
Also published as: FR2439168B1; AU515988B2; CA1126955A; GB2034014B; FR2439168A1; AU5170179A

Abstract

Waste tires are used as fuel in an apparatus for the production of cement by means of a rotary kiln by charging waste tires or crushed waste tire pieces to a position where the temperature of the exhaust gas in the apparatus is 600-1,400 DEG C in an amount of not more than 60% of the total used fuel calculated as heat energy.

Description

SPECIFICATION Method of utilizing waste tires The present invention relates to a method of effectively utilizing waste tires as fuel in apparatus for producing cement.

Recently, the treatment of used waste tires has become a great problem with development of the automobile industry. Waste tires have been partially directly used effectively for fenders of ships and fish factories at sea but the amount of tires used in this way is very small. When waste tires are subjected to burning, public nuisance problems of black smoke, unpleasant odours, and the emission of nitrogen oxides and sulphur oxides occur.

The present inventors having studied the effective utilization of waste tires having a heat energy of about 8,000 kcal/kg, and as a result have developed the method according to the present invention.

The present invention provides a method of utilizing waste tires in an apparatus for producing cement by means of a rotary kiln, which comprises charging waste tires or crushed waste tire pieces as fuel to a position where the gas temperature in the apparatus is 600-1 ,40000 in an amount of not more than 60% of the total used fuel calculated as heat energy.

It is well known that, in the production of cement, combustible substances such as spoil are charged into the production apparatus for effectively utilizing the generated heat in the steps of preheating and calcining the starting materials of the cement or for overcoming the problem of nitrogen oxides, but the combustible substance in this case is a powder. By contrast, the waste tires or crushed waste tire pieces utilized in the present invention have a size of not less than 5 mm. The waste tires directly used without crushing are not limited in the size, if the tire can be charged into the rotary kiln. In general, tires for passenger cars, trucks, and buses are preferable.If waste tires are crushed to a size of less than 5 mm, the particles may be transported by gas flow and are not necessarily burnt at the desired zone, and the temperature of the exhaust gas may be raised and the heat energy not efficiently used, and the fan sucking the exhaust gas may be thermally damaged or agglomeration may occur in a suspension preheater resulting in clogging of the cyclone, and stable operation for a long period of time becomes difficult.

The charging of waste tires as such is more preferable than that of crushed waste tire pieces because finely crushed pieces are burnt near the back of the kiln while whole waste tires enter the inner portion of the rotary kiln and the burning zone is lengthened, so that the reducing state advantageous for reducing the amount of nitrogen oxides (NOx) can be maintained along a long zone. Also, in the case of crushed tire pieces, there is a danger of finely divided powder being formed, so that stable operation for a long time may be adversely affected as mentioned above.Furthermore, it is very difficult to crush a waste tire into a given shape by means of presently known crushers and the crushed pieces have an irregular shape and problems are liable to be caused in the transferring system into the kiln, but in the case of whole waste tires the transferring means presently generally used in a tire factory can be advantageously 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 6000C, they immediately start burning and concurrently a part thereof is subjected to dry distillation owing to the heating and generate reducing combustible substances. The combustible substances reduce and decompose nitrogen oxides generated from the main burner of the rotary kiln by using the starting materials for the cement as catalysts, and the production of cement wherein the exhaust gas is low in nitrogen oxides 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 6000 C, if the crushed particles are fine in size, the particles are transferred to a low temperature zone by the exhaust gas flow, and when the particles are coarse they stay at that position and black smoke is generated due to incomplete combustion and unpleasant odours and nitrogen oxides and sulphur oxides due to nitrogen and sulfur contained in a waste tire itself are generated.

When a waste tire is charged toward a zone where the temperature of the exhaust gas is higher than 1 ,400 C, for example the burning zone at the front of the rotary kiln, it is expensive to obtain finely divided powder. Also, in the case of granular or massive crushed pieces, the burning speed is slow, so that it is difficult to maintain the temperature of the burning zone. In particular, in the case of massive crushed pieces or whole tires, the charging into the burning zone becomes difficult. Accordingly, as regards the apparatus for producing cement using a rotary kiln, 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 of the rotary kiln.In the case of an apparatus provided with a cyclone system of preheater or calcining furnace, the waste tires are charged into a position where the temperature of the exhaust gas is higher than 6000C in the accompanying 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 does not hinder the production of the cement and is not more than 60% of the heat energy of the total used fuel. When this amount exceeds 60%, temperature stability at the burning zone in the rotary kiln becomes difficult to obtain and the quality of the cement is adversely affected and such an amount is therefore not preferable.

In general, a few percent of zinc oxide (ZnO) is compounded in tires during the production thereof 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 sement 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 the amount of unburnt carbon increases, so that coating of the preheater grows and the cyclone becomes clogged.

Therefore, the amount of waste tires or crushed waste tires charged is preferably not more than 1 5%, more preferably 510%, of the heat energy of the total used fuel.

When steel is contained in the waste tires, steel is oxidized at the calcining zone and burning zone and effectively acts as a part of the starting material of the cement.

The present invention has the following advantages.

(1) A large amount of waste tires can be utilized.

(2) Since waste tires are used as fuel, the heat energy of the rubber itself can be effectively utilized.

(3) It is expensive to obtain finely divided tire powder but in the method of the present invention roughly crushed pieces having a grain size of more than 5 mm can be utilized, and the obtaining of such crushed pieces is a simple process.

(4) The quality of the obtained cement is not adversely affected.

(5) Public nuisance due to burning of waste tires does not occur. Indeed, the amount of nitrogen oxides generated in the conventional production of cement can be reduced.

(6) Waste tires can be used directly without crushing, so that this method is advantageous in view of the noise and cost of crushing.

(7) Waste tires including steel can be directly used in the apparatus for producing cement.

The invention will be further described with reference to the following illustrative Examples.

EXAMPLE 1 Waste tires were charged from a feeder of starting material provided at the back of a wet system 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.Tabíe 1. The waste tires contained 20% of steel.

TABLE 1

Experiment Unit 1 2 3 4 5 6 Waste tire size mm - 50-70 150-300 150-300 < 1 150-300 Amount of waste tire used kg/h 0 250 1,000 1,600 250 3,000 Amount of clinker produced t/h 20.0 20.0 20.0 20.0 20.0 Amount of heavy oil used t/h 3.200 3.036 2.543 2.149 3.175 Amount of heavy oil used per amount of clinker buming produced t/t 160.0 151.9 127.2 107.4 158.8 impossible NOx in exhaust gas ppm 500 20 100 80 500 Temperature of exhaust gas in kiln C 700 710 730 750 780 When the size of the waste tires was not less than 50 mm and the amount of the waste tires 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 scarcely varied, the temperature of the exhaust gas of the kiln was high, and in this case the waste tires did not act effectively as fuel. When the used amount was more than 60% of the total used fuel calculated as heat energy, as shown in Experiment 6, the temperature at the burning zone was not stable and burning was impossible.

EXAMPLE 2 Waste tires were charged from the upper portion (gas temperature: about 1 ,0000C) of the junction of the exhaust gas of a kiln and the gas discharged from a cooler, the rotary kiln having a diameter of 5,250 mm and a length of 84,000 mm and being provided with a calcining furnace and a suspension preheater. The obtained results are shown in Table 2. The waste tires contained 20% of steel.

TABLE 2

Experiment Unit 1 2 3 4 5 Waste tire size mm - 10-20 50-100 10-20 < 1 Amount of waste tire used kg/h 0 5,400 5,400 1,000 1,000 Amount of clinker produced t/h 230 230 230 230 230 Amount of heavy oil used t/h 17.20 13,38 13,40 16.53 16.90 Amount of heavy oil used per amount of clinker produced kg/t 75.0 58.2 58.3 71.9 73.4 Temperature of exhaust gas in preheater C 380 390 392 381 410 NOx in exhaust gas ppm 250 200 200 240 250 When the size of the crushed waste tires was not less than 10 mm and the amount of the waste tires used 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 scarcely varied, the temperature of the exhaust gas was increased, and in this case the waste tires did not act effectively as fuel. Since the temperature of the exhaust gas was increased, and in this case the waste tires did not act effectively as fuel. Since the temperature of the exhaust gas was increased, it was impossible to further increase the amount of tires charged.

EXAMPLE 3 A chute provided with an air seal for crushed tire pieces (size: 1 50-300 mm) or tires (diameter: 770 mm, breadth: 195 mm) was provided at the side of a chute for starting material entering four stages (iowest stage) of a cyclone of a rotary kiln (NSP) having a diameter of 5,2 50 mm and a length of 84,000 mm and provided 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: 1 50-300 mm) were charged from a starting material feeder provided at the back of a rotary kiln (WFB) having a diameter of 3,450 mm and a length of 66,300 mm and provided with a wet system boiler into the kiln.

In both cases, the tires contained 20% of steel and the heat energy of the tires was 7,500 kcal/kg, which corresponds to 77% of the heat energy of 1 kg of heavy oil.

The obtained results are shown in Table 3. As regards the quality of the cement, gypsum was added to the obtained clinker so that the SO3 content in the cement became 2.2% and the mixture was crushed with a laboratory pot mill 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.

TABLE 3

Experiment 1 2 3 4 5 6 7 8 9 Kind of rotary kiln N S P W F B Amount of waste tire charged calculated as heat energy, % 0 5 10 15 20 0 10 per time, kg/H - 1,140 1,140 2,280 2,280 3,420 4,500 - 420 Shape of tire crushed tire crushed tire crushed crushed crushed piece piece piece piece Production of clinker (t/H) 230 230 230 230 230 230 230 20.0 20.0 Amount of heavy oil used (t/H) 17.20 16.48 16.51 15.7 15.79 14.88 13.89 3.20 2.88 Amount of heavy oil used per amount of clinker produced (kg/t) 74.8 71.7 71.8 68,3 68.7 64.7 60.4 - Temperature of exhaust gas in kiln ( C) 380 380 380 382 381 386 391 700 700 NOx in exhaust gas (ppm) 250 240 220 240 190 230 200 500 200 Quality of cement Setting time: Start (hour-minute) 2-17 2-22 2-20 2-55 3-00 3-50 8-30 2-15 2-15 Finish (hour-minute) 3-09 3-28 3-25 4-00 4-15 5-25 11-00 3-20 3-55 Strength of mortar 28 days, kg/cm2 405 403 407 408 415 432 510 411 430 As seen from Table 3, when the amount of waste tires 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. Coating growth of the preheater and clogging of the cyclone owing to increase of unburnt carbon occurred frequently and continuous safe operation for a long period of time became difficult. Accordingly, the amount of waste tires charged was preferably not more than 1 5% of the total used fuel calculated as heat energy, and was more preferably 510% taking the saving of the amount of heavy oil into consideration. In comparison with the use of crushed waste tire pieces, when the tires are charged directly the growth of coating of the preheater and clogging of the cyclone did not substantially occur and the temperature of the exhaust gas did not increase.

Furthermore, a rotary kiln (SP) provided with a suspension heater, which was not provided with the calcining furnace, showed similar results to the NSP kiln.

Claims

1. A method of utilizing waste tires in an apparatus for producing cement by means of a rotary kiln, which comprises charging waste tires or crushed waste tire pieces as fuel to a position where the gas temperature in the apparatus is 600--1,4000C in an amount of not more than 60% of the total used fuel calculated as heat energy.

2. A method as claimed in Claim 1, wherein the amount of waste tires or crushed waste tire pieces is not more than 15% of the total used fuel calculated as heat energy.

3. A method as claimed in Claim 2, wherein the amount of waste tires or crushed waste tire pieces is 5 to 10% of the total used fuel calculated as heat energy.

4. A method as claimed in any of Claims 1 to 3, wherein waste tires are directly used without crushing the tires.

5. A method according to Claim 1 of utilizing waste tires, substantially as herein described in any of the foregoing Examples.