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Solid Recycled Fuel FAQs

The aim of these FAQs is to answer some of the basic questions relating to the potential use of Solid Recovered Fuel (SRF); particularly in the Indian Cement Industry.

What is SRF?

SRF is the name that is given to an alternative fuel that is widely used in the European Cement Industry and stands for Solid Recovered Fuel. SRF is a waste derived fuel which is made using household residual and commercial waste, therefore re-using valuable materials that would otherwise have been wasted. It looks like shredded paper and consists of paper, cardboard, wood, carpet, textiles and plastics. The material has been subject to a treatment process to remove biodegradable matter and produce a solid, clean and non-hazardous fuel. The fuel is manufactured to a tight specification by specialist companies so that it is suitable for use as a fuel in cement kilns.

Why is SRF an ideal fuel?

SRF is an ideal fuel for the cement industry as it has similar properties to some of the fuels that already used in the cement industry. The size of SRF – normally around 20-30mm flat pieces of plastic or paper – means that it burns rapidly, releasing the heat into the cement manufacturing process where it is needed. Using SRF will save valuable fossil fuels such as coal, heavy fuel oil and gas. As the components that make up SRF are carefully monitored, in most cases the variability of parameters such as moisture, ash and chloride will be lower than in fossil fuels such as coal.

In addition, as compared to industrial waste, lack of supply is never an issue given the large quantities of household residual and commercial waste generated each day.

How does the calorific value (CV) compare to coal?

Dependent upon the proportions of materials such as paper and plastics, the CV of the SRF can be tailored by the producer of the SRF to suit the requirements of the cement manufacturer. However, a typical SRF would have a net CV of between 18 and 20 MJ/tonne. Whilst there are many different grades of coal available in India, it is understood that a typical CV of coal used in the cement industry would be a blend of Indian and International coal with a blended CV of around 17 MJ/tonne. Therefore it can be seen that, in terms of CV, SRF could be substituted on a like-for-like basis with coal.

What are the properties of SRF?

In relation to the cement manufacturing process, the following parameters have been reviewed:

  • Moisture content – SRF contains around 10-15% moisture. Clearly this is higher than in pulverised fuel that is used in the cement manufacturing process. If fired in the main burner in the kiln experience shows that it does not have a major impact as the SRF is only a partial replacement of the coal, which is the principal fuel in the burning zone. If SRF is used in the calciner almost no impact is observed, as the calciner vessel of the pyro-processing line is ideal for lower grade fuels.
  • Chloride – SRF can contain up to 2% chloride due to the plastics fraction in the fuel; however, the SRF is designed to have a chloride content based upon the total chloride inputs into the pyro-processing system up to a level where build-ups in the process can be avoided. More typical levels of chloride in SRF are around 0.5 – 1%. A chloride balance can be performed to identify the maximum level of chloride for a particular SRF addition rate. Many manufacturers who are using high levels of chloride have installed volatiles by-pass systems to remove chlorides.
  • Sulphur – SRF contains almost no sulphur and therefore is particularly advantageous in plants that have high levels of sulphur in the process as it will reduce the overall sulphur input into the process.
  • Ash – SRF contains up to 10% ash, which is not dissimilar to the coal mix that is currently being used in Indian cement plants.

Are there any residues left over when using SRF?

As with coal, there are no residues remaining from the use of SRF. All of the ash is incorporated into the clinker. SRF will be delivered wrapped in plastic bales; this plastic can be recycled locally in India.

What happens to emissions when using SRF?

There should be no change in emissions when substituting coal with SRF. The material is finely shredded and therefore burns rapidly in the high temperature of the kiln ensuring complete combustion of the material and therefore no change in CO or VOCs. The use of SRF should have no effect on NOx as the majority of NOx produced in a kiln is thermal NOx. Due to the low sulphur in SRF, no change in SO2 emissions will occur.

How can SRF be used?

SRF is being successfully used in many cement kilns within Europe and can be adapted to many different process types. SRF is being used on the main burner on Lepol and preheater kilns and both the main burner and in the calciner in precalciner kilns. When used on the main burner in the kilns, it is usually burnt with another fuel such as coal which supports the use of the SRF and maintains the flame shape. When used in the calciner it can be used with a blend of other alternative fuels or on its own.

What kind of system needs to be installed to use SRF?

When SRF is used on the main burner in the kiln, it is necessary to transport the fuel into the kiln via a pneumatic transport system.

When SRF is used in the calciner, it can be transported into the kiln either by a pneumatic transport system or a mechanical transport system.

Firing SRF mid-kiln, using a technology called MIFLEX, is the better solution for long dry and wet kilns. It has the added advantage to be able to co-fire other bulk fuels like tires simultaneously.

The right solution, including the investment costs, will depend on the existing process parameters, feed rates, plant lay-out etc.

No system is particularly complicated, with the most important item in the system being the volume control, so that the fuel can be metered in at the correct weight. The systems are independent of the coal system i.e. the SRF is not mixed with the coal prior to injection into the kiln or calciner.

Why ship SRF from the UK to India?

SRF is being produced in the UK for use in cement kilns and there is a surplus of material. Due to the cost structure of disposing of these materials in the UK, the fuel can be produced at extremely low cost and therefore provides a suitable alternative fuel for the cement manufacturing process. From the Indian perspective, there is a shortage of coal for the production of both power and cement which means that expensive international coal needs to be imported into the country.

Therefore SRF represents a real opportunity for the cement industry. Whilst the materials that make up SRF are available in India, they are potentially more valuable to be recycled/re-used elsewhere rather than used as a fuel for cement kilns.

Where else is SRF being used?

SRF is being extensively used throughout the United Kingdom and Europe as a substitute fuel in cement kilns. SRF is widely transported between countries in Europe where there is a surplus of material in one country and a demand in another. All of the major international companies such as Lafarge, Holcim, CEMEX, Italcementi and Heidelberg are using SRF in Europe and SRF is taking over from other alternative fuels such as tyre chips.

What about CO2 emissions and carbon credits?

The use of alternative fuels in the cement industry saves fossil fuels that would have otherwise been burnt. Within Europe, alternative fuels that have a biomass content will have a proportion of their CO2 emissions classed as carbon neutral when annual CO2 emissions are calculated. SRF contains around 50% biomass and therefore only 50% of the CO2 emissions from this fuel would be counted in an emissions trading scheme. Outside of Europe, alternative fuels projects which demonstrate a reduction in CO2 through the use of biomass may fall under the Clean Development Mechanism (CDM) of the UNFCCC. Under this scheme, carbon credits (which could be sold on the open market) would be obtained upon implementation of the alternative fuels scheme. This scheme would have to be reviewed on a case by case basis.

What are the applications of SRF?

Used for energy recovery and it is generally used for the following thermal conversion processes:

  • Co-combustion in coal fired boilers.
  • Co-incineration in cement kilns.
  • Co-gasification with coal or biomass.

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