Solid Recovered Fuels – Specifications and classes
A main pillar of waste management in the EU is the waste hierarchy. According to the hierarchy generation of waste must be prevented, otherwise waste should be reused, recycled, recovered or disposed of in that sequence. Despite high recycling potentials, not all waste can be turned into secondary materials. If it is about combustible waste, incineration is a proper way to dispose of waste. Another option for such waste is to process it into Solid Recovered Fuel (SRF). SRF can be used in specific applications such as cement kilns, CHP plants and power plants. Such use results in higher efficient use of the calorific value of waste and a significant CO2-reduction by substituting fossil fuels like hard coal and lignite.
The good value of SRF as a vital element for waste management and as source for sustainable energy has been recognised by the European Commission. It has therefore mandated CEN to develop standards for SRF. These standards must support the production and use of SRF. The use of SRF requires a stable supply of pre-treated and homogenised waste upgraded to a fuel quality that can be traded amongst producers and users of SRF.
From the several technical standards developed by CEN/TC 343, EN 15359 is amongst the most crucial. EN 15359 provides for a system of specification and classification of SRF. It also provides for a set of compliance rules that points out how SRF can be characterised in a reliable way. This current document gives explanation to the use of EN 15359. Further information can be found in the Technical Report (CEN/TR 15508).
Prior to the development of standards, waste derived fuels (RDF) were produced and used in a rather uncontrolled way. Producers of RDF used own ways of analysing and characterising their products. Users of RDF are from various kinds of industries. Each sector or even each individual company would have its own way of specifying the type of fuel it wished to buy.
There were thus many ways of describing the characteristics of RDF and each way would actually only fit for a single couple of producer and buyer. If SRF were to become a real market, a common language had to be developed. This common language is actually what EN 15359 and all the other European Standards of CEN/TC 343 are about.
Standard EN 15359 provides for tools with which SRF can be described in detailed (specification) or in general (classification) technical parameters. Main points of departure for the standard were:
It must describe actually produced SRF, however with the restriction that merely SRF may be covered by the standard that can be used in installations that meet the requirements of the WID.
SRF should not be used as a fuel if there is less thermal energy produced from the combustion of the SRF and available for the process of the installation, than the energy used by the combustion of the SRF ( there should be a calorific gain)
3 The mandate
CEN was mandated by the European Commission (through mandate M/325) for the following:
To develop, as a first step, a set of Technical Specifications concerning the use of SRF for energy recovery in waste incineration or co-incineration plants
As a second step to transform this set of Technical Specifications into European Standards
Importantly, the mandate refers to incineration and co-incineration of SRF as waste. These operations are both covered by European Directive 2000/76/EC (Waste Incineration Directive – WID). The mandate emphasises that the Directive aims to set stringent operational conditions, technical requirements and emission limit values for plants incinerating or co- incinerating waste in order to achieve a high level of environmental protection and human health protection. The use of SRF in such plants will therefore always occur under such stringent conditions. A high level of protection of the environment and human health protection is therefore secured for all SRF produced according to EN15359.
4 Contents of EN15359
EN 15359 provides for methods of specification and classification of SRF. These issues are subsequently described below.
The standard prescribes the specification of certain physical and chemical properties. These properties must be established by making use of testing and analysis methods also developed by CEN/TC 343. The properties obligatory to specify include particle form and size, moisture content, ash content, net calorific value, chlorine content and each heavy metal mentioned in the Waste Incineration Directive and the sum thereof. Also SRF class and origin are obligatory to be specified. This means that for each SRF produced all relevant heavy metals must be specified. Producers are obliged to use the prescribed form of the standard to specify SRF.
The standard also provides for a form that can be used for properties that are not obligatory to specify. These include for instance biomass and ash melting behaviour.
The aim of classification is, as the name suggests, classifying SRF. That is, a class is assigned to a certain SRF. As the method of specification already provides for the full information of a SRF, classification only aims to assign it to a class so that both producer and user understand the type of SRF that they are dealing with. Classification is a simplification of specification. One identifies a limited set of main properties that in one glance give decisive information about the quality of a SRF.
Classification does not differ between “good quality” SRF and “poor quality SRF”. It is an error to think that discrimination is a goal of classification. Classification is applied to put any SRF in a “cell” and to give a global view on all existing SRF’s. There is a hidden, but still a major contribution of classification to a high level of protection to the environment. Because each SRF can now be classified, it will become very clear at a quick glance which SRF has indeed poor environmental properties and may need special raw-gas cleaning technology. Users can decide on that basis about the type of SRF to be used and the technologies to be applied.
CEN/TC343 has chosen to use the following three properties to quickly describe (or classify) a SRF:
Net calorific value (NCV)
NCV is an indicator of the market value of SRF. NCV also indirectly gives an impression what type of SRF is involved. NCV is the most important property of SRF as it describes its value as a fuel.
Chlorine is unwanted in SRF as it contributes to corrosion. High chlorine content will lower the market value.
Of all relevant heavy metals, Hg is selected as an indicator of the environmental quality of a SRF. Because of its high volatility, Hg is the heavy metal most likely to be emitted. LCA studies identify Hg as an important factor of SRF. All available SRF data as well as LCA studies proof that Cd and Tl are of limited relevance. There is therefore no added value adding Cd and Tl as classification parameters. Although the classification system focuses on Hg, all heavy metals according to WID are obligatory parameters for specification according to EN 15359.
The set of three classification properties gives an immediate and rather reliable impression of the overall quality of a SRF. Based on these three properties, a buyer can quickly assess the type and quality. The properties each give information concerning a different aspect of SRF (NCV: basic property as a fuel, Cl: potential corrosion effects, Hg: environmental quality). The three properties do not give comprehensive information that has to be provided for on a specification form.
Per property mentioned, five classes have been established. Per property SRF can be classified according to the following table.
The classification scheme is compact and comprehensive so that each type of SRF can be classified according to a set of three parameters/digits. Relevant to mention is that classification has been validated in the Quo Vadis project.
5 What’s outside the scope of the standard
The standard does in no way regulate all issues about SRF. As stated above, the CEN/TC 351 standards are technical standards. EN 15359, on top of that, provides for a framework how to communicate the results of testings carried out according to the technical standards. The standards, and EN 15359 specifically, do not regulate in any sense the conditions under which SRF is used in incineration or co-incineration plants. These conditions are set out in the permit of the SRF-using plant.
In particular, EN 15359 does not regulate which type of SRF may be used in which type of incineration or co-incineration plant. Such conditions are set by the competent authority. Setting limit values for contaminants in SRF is not an issue demanded by the mandate. The mandate requires specifications of a range of parameters. It is up to the competent authority to decide which levels of contaminants will be accepted. In deciding so, the competent authority will take account of the emission limit values set in the Waste Incineration Directive and of best available technologies described in BREF documents.
It is sometimes argued that EN 15359 “allows for a high chlorine content < 3 % and for low net calorific value > 3 MJ/kg”. As explained above, EN 15359 does not set limit values. It is therefore wrong to think that EN 15359 could in any way “allow” an SRF. The classification scheme only visualises that SRF with high chlorine content or low net calorific value may exist. It is up to competent authorities to decide if such SRF is “allowed”.
6 What is beyond specification and classification
It is sometimes argued that, notwithstanding the above, some member states do actually set limit values for contaminants. This is true for member states which have a longer history of using SRF than Europe in general. In these member states the next step in the management of SRF has been taken: certification. One should not mix up specification/classification with certification.
If Europe wants to properly make use of SRF, then finally a system that distinguishes between “good” SRF and “lower grade fuels” may be necessary. Such a distinction can only be made on the basis of a system that includes limit values for contaminants. Such a system can only work and be maintained when a sound structure of certification is laid as a basis. In its turn, a proper certification system can only exist when there is a good set of technical standards, including a standard for specification/certification. Put in another way: limit values can only be set and risks can only be managed when there is a proper standard for specification/classification.
The next step to take is then the development of certification schemes that include limit values. An example can be found in the German RAL-GZ 724. Specification/classification will help to identify in a quick way and first approach which SRF will be within the limits and which SRF will be out. Therefore EN 15359 will be of great help for authorities when setting appropriate limit values for (co-) incineration.
7 EN 15359 is not the end of waste
On EU level several steps are now taken to develop end-of-waste criteria for specific categories of waste according to article 6 of the Waste Framework Directive. A certain waste may only cease to be a waste if:
the substance is commonly used for specific purposes,
a market or demand must exist,
the substance fulfills the technical requirements for the specific purposes and meets the existing legislation and standards applicable to products
use of the substance will not lead to overall adverse environmental or human health impacts
Any misunderstanding with regard to the end-of-waste status can not be ascribed to EN 15359 and the classification system. Such misunderstanding can only be ascribed to improper understanding of sense and use of a classification system. The question whether certain types of SRF may deserve a product status cannot be answered by using EN 15359 exclusively, but EN 15359 will be a useful tool. Per definition a classification system has to cover all existing materials to be classified. It is obvious, that not all kinds of SRF can be classified as a product. In that sense the task of a classification system and the question of the status of a SRF are not congruent. The question of a product status of a SRF has to be discussed within the European legal framework and based on LCA’s. Classification is an important tool but not enough to decide about end-of-waste status.