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Tyre Burning - Ten Years of Experience

F. Marecha]

Cimenleries CBR

Introduction: The CBR Group

For more than half a century, the CBR Group has been serving the construction industry network of operations in cement and building materials.

CBR has continually expanded and restructured its operations to customers.

The company holds a leading market position in Belgium; The Netherlands, Rhin' D, lai Westphalia, the Western Provinces of Canada, the West Coast of the United States and South Bohemia and Moravia in Central Europe.

The core business is Cement, Aggregates and Ready-mix Concrete for a world capacity of :

Cement: 15 miotpy in 18 cement plants,

more than 70 quarries with annual output of 29 miotpy

about 200 ready-mix concrete units for 9 mio m3 per year.

Four kilns are burning waste tyres :

1980 : Lixbe (Belgium) : whole lyres

1986: Redding (California) : rubber chips and whole tyres

1986 : Mokra (Czechoslovakia) : whole lyres

1988 : Tilbury (Canada) : rubber chips.

The quantity used is about 60.000 tpy.

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Tyre Burning • Ten Years of E~perieoee

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Clinker burning operation

The clinker production includes two chemical reactioDS :

lime production: decarbonation of CaC03 al about 8S0·C clinker formation in the kiln sintering zone above 1400·C

Nowadays, the clinker production process is done by preheater and preheaterl prccalciner systems. The wet process was replaced progressively in the seventies because of its high heal consumption.

There is a major difference between preheater and prebeater/prccalciner kilns in terms of lyre burning possibilities.

For pre heater kilns, the level of decarbonation of the meal at kiln inlet is lower than with a flash calciner. Besides, the calciner kiln design is oompletely different:

for a prehcater kiln, all the combustion air passes through the kiln

for a precalcinerkiln, tbe major part of the combustion air (60 %) passes through the tertiary air duct aJong the kiln. This is the reason why those kilns are smaller in diameter for the same rate of production.

Generally, the tyrc burning energy is used for meal decarbonation. To bum lyres, it is necessary to have a significant combustion time which is only possible inside the rotary kiln if oxygen is carried by the process combustion gases.

The preheater kiln is tbe typical design for tyre burning because :

there is room for the tyre heat flow inside tbe kiln to finish the meal decarbonation

there is oxygen inside tbe kiln wbich is designed for the fuU combustion air flow

The lyre combustion is called an air through (AT) precalciner system for preheater kiln.

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Tyre Burning · Tea Yean of ~perieoc:e

PREHEA TER KILN

Chipped whole tyresl . or others fuels J moxlmum 207.

, , I Time of decorbonotion

",', bun'~ 80% of energy

ITI I % on dry basis

~=====~ in the kiln (> 1 minute) , . . ... ~O . . .. , . _ ,

with tyres in oir ~---i.. /'. / through ~ombU$tion ''' '' " . ' . '"' . • . ;.51)" C

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Co S = 1c,0~ Sio.. ~A _ CoO Al. ~

C. Af= Coo . AI,. 0.. Fe:. Q.

Conclusion: Long time to burn tyres in the zone into the ki ln.

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Tyre BumiDg· Tea Yean of Experieoc:e

PREHEA TER PRECALCINER KILN

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% on dry basis ~TIme of decarbonation I lin the kiln (seconds) Temperature·C I I I I

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o 5 10 15 Residence time in

20 minutes the knn

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Conclusion : No t ime t o burn tyres in the decorbonotion zone because of the flash co lciner.

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Process description

As an example, we consider a 1 miotpy prebeater whole tyre burning line as the "stato-oll-tl art W system.

The design capacity of the tyre feeding system is 2.5 tpb. For an average weight of 7.5 kg/,y" feeding rate is one tyrc every 10 seconds in the Idln feed hood.

Such an installation should bum between 15.000 and 20.000 tons of tyres per year.

In function of the tyres. the tlow-sbeet is :

Tyre storage: tbe tyre storage is limiled in quantity per pile which bas to be fin, P'''''''it~

From the storage, a special equipped payloader feeds a hopper once a shift (capacity or 12 tons).

The hopper botto m is an hydraulic powered sliding bottom which pushes the tyTes of cooveyors.

Those conveyors (about 15 units) separate tbe lyres by starting and stopping anel 50' avo;, any tyres to be clinched together.

When the lyres arc separated, a linear television camera controls the shape of the rejects all material out of the requested shape (minimum and maximum diameter, lyres, etc ... ). The rejected material bas to be used as shredded material .

When controlled for size: and shape, the tyreS follow a series ·of conveyon: which kiln consumption and the extraaio n flow.

Each tyre is weighed and the flow is adapted to the set point through a 5Of~" integrates the weight and compares it to the requested flow.

From this point on, the tyre is conveyed to the kiln feed hood with an inclin,.! (belt pocket conveyor, chain with hooks, etc ... ). The conveyor type depends __ ,_ ; space in the plant lay-out.

The tyre is fed to the kiln through a profiled chute with a double gale to avoid the system. The chute profile is designed to put the tyre in the kiln (rotary plUtJ{

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Tyre BunUng - Ten Y ~ of Experieoce

Camera to control the size Conveyor to the kiln chute

Weighing system

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Effect oftyre burning 00 stack cmissioos

The steel inside the tyres becomes oxidized in the ldln and contributes to a part of content in the clinker.

The organic components are burned into the kiln and in the riser duct at high (1200"C).

Many stack measures are available in the Group to com~ the emission with orw;'~oq,. f.

Here are the practical results :

Dust emission: No influence of lyre burning. The dust collector is an electrostatic precipitator or a bag house filter.

Heavy metals: No difference with or without tyres - The data are below significant limits of detection ..

502: No influence because the sulphur oftyres is included in the sulphur cycles of the kiln. The hot meal may contain up to 5 % of 503, this S03 coming from raw materials and fuels is ; taken from the kiln by the clinker which contains up to 1 % S03 in some cases. This S03 is a part of the sulphate used as cement component to control the cement setting (a nonnal cement contains 5 % of gypsum).

NOx : The NOx emission is reduced in all cases when using lyres. The reason is the combustioo of tyres at lower tempeT3tures than the fuel in the main burner (the higher the flame temperature, the higher the NOx emission). The result is the same when the tyres are replaced by coal or gas in riser duct burning systems.

Organics: They remain under the limits of detection.

Scrapped tyre disponibility

If we take the ratio of 1 scrapped tyre/yearrmhabitant (or 7 kg/year) as well as a consumption of 350 kglyearrmbabitant, the possibilities of the cement industry can

':<"

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SO % of prebeater kilns

150 kglyearftnhabilant with tyze burning possibilities

15 % energy from tyres

800 kcalJkg clinker, or 120 kcalJk:g cement from tyres

Heal flow possible for cement from tyres per inhabitant/year : ISO x 120 = 18.000 kca1

Heat cootenl per tyre : 8.000 kcallk:g

Heat flow possible from scrapped tyres per inhabitant/year : 7 x 8.000 = 56.000 kca1

The cement industry could use less tban 50 % of the total energy coming from old tyres.

CooclusioD

The lyre burning in the clinker kiln is a perfect process to eliminate scrapped lyres.

steel is used as clinker iron oxide component,

sulphur is combined to clinker and is a part of the gypsum added to cement in the finish grinding process,

NOx is reduced at the stack because of the lower burning temperature of the 15 % tyres used as fuel.

No Significant differences are detected (or other poUutants with or without lyre burning.

The cement industry could usc about 50 % of the scrapped tyres in the prebcater kiln type.

Commission of the European Communities Directorate-General for Energy (DG XVII)

*** * * * THERMIE * * * ***

European Seminar on

IMPROVED TECHNOLOGIES FOR THE

RATIONAL USE OF ENERGY IN THE

CEMENT INDUSTRY

Ministerium fUr Wirtschaft, Mittelstand u. Technologie

Potsdam Germany

Berlin, 26-28 October 1992

PROCEEDINGS

GOPA - Consultants Bad Homburg

Germany

LDK Consultants, Engineers & Planners

Athens Greece

Members of the OPET Network (Organisation for the Promotion of Energy Technologies)

With the Cooperation of CEMBUAEAU - The European Cement Association