Net calorific value

Although granulates obtained from used tyres are not used for energy

recovery, Aliapurs Research and Development department

wanted to study their net calorific value and thus establish the reference

data that was not at the time available for this type of product.

These data could also be re-used for recycling sport and leisure surfaces,

the granulates of which have reached their end-of-life phase.

In this case, energy recovery would become an imaginable solution.

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DefinitionNet calorific valueQuantity of heat released during the complete combustion of one cubic meter of gas under normal temperature and pressure conditions (1.01325 bar or 101 325 Pascal at 0C) when the water formed during combustion remains as steam and the combustion products are evacuated under normalised test conditions.In French: pouvoir calorifique infrieur.

Combustion is the chemical reaction that occurs between a fuel and a combustion agent, for example oxygen in the air in the presence of a heat source. The result of complete combustion is essentially carbon dioxide (CO2), water (H2O) and heat.

Calorific value

Reference valueThe net calorific value of ELT granulates is 35 MJ/kg.

How is the calorific value calculated?The fuel sample is placed in a sealed steel cylinder called a bomb calorimeter, with pure oxygen. The water formed during combustion is liquid and vaporises, a change of state that requires energy. The total quantity of heat generated by combustion, known as the gross calorific value (GCV) is thus equal to the heat released by the combustion, to which is added the heat needed to vaporise the water.

In reality, water vapour generally condenses on the outside, particularly when it comes out of the chimneys of industrial or domestic apparatus. The quantity of heat produced during combustion is thus lower than the gross calorific value, as the water vaporisation heat is not recovered.The net calorific value (NCV) is calculated by subtracting from the GCV the water vaporisation heat. This is more characteristic of the quantity of energy provided by the fuel under consideration.

For gaseous fuels, the NCV is a value around 90% of the GCV. It is expressed in megaJoule per kilo (MJ.kg -1 or MJ/kg).

Projects for standards with regard to analyses of solid recovery fuels are currently being studied. Aliapur hopes to validate the analysis methods specific to ELT for harmonisation with the other processes implemented, even if used tyre granulates are the subject of material recycling.

The calorific value is the quantity of heat released by the combustion of one kilogram of fuel, or a cubic meter if it is a gas.

(C, H) + O2 CO2 + H2O + heat A compound composed of

carbon and hydrogen reacts with the oxygen

to produce carbon dioxide,water and heat

C3H8 + 5 O2 3 CO2+ 4 H2O + heat Example of propane

500 kg

ELTgranulates

Operating methodThis method was established using the NF ISO 1928 (May 2004) standard.

The samples of ELT are prepared from micronisation of the granulates contained in 1.8 g samples. These samples are themselves obtained, by means of a rotating divider, from 500 g taken from a big bag of 500 kg.

Method recommended and studied by Aliapur

The micronised ELT granulates sample (0.3 g) is placed in a bomb calorimeter filled with pure oxygen. The bomb is then placed in a calorimeter filled with distilled water and equipped with a stirring device and a thermometer.

After measuring the initial temperature, combustion is started inside the bomb. Changes in the water temperature of the calorimeter are monitored for the duration of the experiment. These changes are directly linked to the heat released by the combustion, that is, the calorific value of the sample.

This equation means that the calorific value of the sample is equal to the total mass (mass of the water in the tank + equivalent mass which is constructors data) multiplied by the specific heat of the water multiplied by the difference between the initial temperature and the maximum temperature attained during the experiment, all divided by the mass of the sample.

The reference studies have shown that the preparation of the sample (reduction followed by micronisation) guarantees better reproducibility of the measurement than direct use of non-micronised granulates. The tests and results obtained confirm the choices made in terms of analysis method and preparation and sampling protocol.

CVsample = mtotal x HCwater x Ttotal

msample

500 g sample

Sample composed using the heavy method

see Samples and sampling sheet

Reduction of the sample using a rotating divider = 1.8 g

Micronisation at 500 m taken from the samples = 0.3 g

Method recommended and studied by Aliapur Example of a device

Calorimeter

Tank

Cover

Bomb + coverCell

Stirrer

Weighing the mass in the tank Taking the sampleMicronisation at 500 m taken

from the samples = 0.3 g

Putting the cover in place Measuring the temperature at the end of the test

FILIRE DE VALORISATION DES PNEUS USAGS

Regardless of the samples tested (granulate essentially obtained from truck tyres, passenger car tyres or a mixture), the NCV was 35 MJ/kg.

Examples of NCV

n Dry wood: 21 MJ/kg

n Coal: 24-29 MJ/kg (coal comes in a range of different qualities)

This operating method is currently the subject of a study with a view to establishing a standard.

Results

In cases where tyre granulates could not be used for material recycling, for example when recycling play areas, synthetic turf, etc., it was nevertheless possible to use them as fuel thanks to their truly remarkable NCV

Conclusion

Net calorific value

ALIAPUR - Research & Development71, cours Albert Thomas - 69003 Lyon - FRANCETel: +33 (0)4 37 91 43 20 - Fax: +33 (0)4 78 54 67 14www.aliapur.fr - contact@aliapur.fr

USED TyRE RECOVERy IN FRANCE

References

Reference studiesn Caractrisation de granulats de PUNR CTTM1 pour Aliapur Fvrier 2007.n Etude et analyses de granulats de PUNR LRCCP1 pour Aliapur Juin 2007.

Standardsn PR CEN/TS 15400 Solid Recovered Fuels Methods for the Determination of Calorific Value.

n NF ISO 1928 Mai 2004 Solid mineral fuels Determination of gross calorific value by the bomb calorimetric method and calculation of net calorific value.

A project for a standard concerning solid recovered fuels is currently being studied for ELT shred. Aliapur thus hopes, in an attempt to harmonise methods, to validate these methods on ELT granulates even though most granulates are used for material recycling.

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(1) Centre de Transfert de Technologie du Mans (CTTM) et Laboratoire de Recherches et de Contrle du Caoutchouc et des Plastiques (LRCCP).

The studies carried out by Aliapur were based on a variety of batches of ELT granulates from four European granulation factories using different processes and raw materials. These batches correspond to the main products marketed by these sites.

The four sites from which the samples were taken collectively represent the main configurations of what can be found in terms of processes and types of tyre used. Aliapur used a wide variety of products for its analyses, guaranteeing an overall view of the sector and good representativeness of the results.

Sample sites

4

n Factory 1: successive shredding of truck tyres.

n Factory 2: successive shredding of passenger car tyres.

n Factory 3: shredding by crushing of truck and passenger car tyres.

n Factory 4: cryogenics followed by shredding of truck and passenger car tyres.

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Net calorific GB2