The objectives of the project were to undertake a survey on the current practices of production and use of refuse derived fuel (RDF) in the fifteen Member States of the European Union, as well as to undertake an overview of the legal and policy framework of RDF production and use; an assessment of the environmental impacts and of the economic aspects and a review of alternative outlets if the waste streams were not used to produce RDF.
It was agreed at the project inception meeting, that for this project, the term ‘refuse derived fuel' would encompass any waste that is traded and co-burnt in installations for power generation or in a manufacturing process where heat is required (e.g. cement production).
High calorific fractions from processed municipal solid waste (MSW) and industrial wastes are being used both in dedicated energy-to-waste plants and as fuel substitutes in industrial processes. There is no detailed information on the current scale of these practices across Europe.
It is argued that RDF co-incineration in industrial processes has several advantages such as saving non-renewable resources by substituting fossil fuels in high-demand energy processes. However there are concerns over the discrepancies between the controls applied on dedicated incineration and co-incineration plants and argument that it encourages their removal from the material recovery/re-use cycle, thereby going against the waste hierarchy which rates waste prevention/minimisation and recycling as being preferable to energy recovery and disposal. On the other hand, some argue that using RDF in industrial processes compared with bulk incineration has a flexibility advantage as to optimise economic performance, incinerators must be fed with a constant through put of waste which could in certain cases hinder the development of prevention or recycling initiatives.
There is a lack of environmental assessment information about these practices and the economics driving the production and utilisation of RDF are also unclear. This study is intending to provide this information.
III MAIN FINDINGS
Refuse derived fuels cover a wide range of waste materials which have been processed to fulfil guideline, regulatory or industry specifications mainly to achieve a high calorific value. Waste derived fuels include residues from MSW recycling, industrial/trade waste, sewage sludge, industrial hazardous waste, biomass waste, etc.
The term ‘Refuse Derived Fuel (RDF)' in English speaking countries usually refers to the segregated high calorific fraction of processed MSW. Other terms are used for MSW derived fuels such as Recovered Fuel (REF), Packaging Derived Fuel (PDF), Paper and Plastic Fraction (PPF) and Processed Engineered Fuel (PEF).
The terms ‘Secondary Fuel', ‘Substitute Fuel' and ‘Substitute Liquid Fuel (SLF)' are more commonly used in reference to industrial waste fractions such as tyres or solvents processed to achieve consistent quality compatible with particular process requirements.
Policy and legal framework
Under EC law, the manufacture of RDF from waste does not change the status of the material. This implies that the movement and utilisation of RDF is subject to waste licensing. However, R1 – one of the ‘Recovery Activities' as defined in Annex IIB of Directive 75/442/EEC as amended, implies that where waste is used ‘principally as a fuel or other means to generate energy', Member States can under certain conditions exempt from licensing such processes.
An important EC Directive which has an impact on RDF market is the Landfill Directive 1999/31/EC which requires diversion from landfill of biodegradable fraction of MSW and used tyres. Member States will have to introduce either source-separation or implement waste sorting plants to separate biodegradable fraction from MSW or alternatively divert the waste to other treatment methods such as incineration. The residual fractions from such sorting plants can typically be converted into RDF, as it is a drier solid fraction usually with a higher calorific value. This is why RDF production is viewed in some countries as a strategic component of their integrated waste management policy in order to comply with the Landfill Directive recycling targets. Even in countries where source separation is not yet well-developed or where mass burn incineration is predominant, RDF production finds some support as it offers more flexibility in waste management to accommodate continuing progress in minimisation, re-use and source separation for recycling. Similar arguments are advocated by local authorities lacking hazardous incineration capacity and which rely on co-incineration of industrial hazardous waste as part of their waste management strategy.
The other important piece of EC legislation that will impact on co-incineration of waste is the new Waste Incineration Directive 2000/76/EC which aims to bring closer the requirements for incineration and co-incineration. The Directive appears to move matters in the right direction, but it has left divergence between these two processes in the requirements for emission control equipment. For example, air emission limit values for dust, NOx and SO2 emissions are less stringent for cement kilns than for incinerators.
Another interesting point is that the New Incineration Directive imposes the same limit values for incineration and for co-incineration of ‘untreated municipal waste'. The term ‘untreated' is not defined in the Directive and will need to be clarified. This could have a positive impact on the increase in pre-treatments of residual waste, especially those designed to enhance the homogeneity and calorific value of the fuel fraction and thus encourage RDF production.
The Renewable Energy Directive 2001/77/EC is likely to have an impact on RDF markets for biomass waste (paper, organic) and a possible knock on effect on incineration as the Directive aims to promote the use of renewable energy such as biomass waste. Key additional policy variables in this context are those related to climate change. Climate change policy may increase the benefits associated with fossil fuel displacement from waste derived fuels on the basis that greenhouse gas emissions are displaced. This is why RDF is viewed in some countries as part of their strategy to help them fulfil the requirements and commitments of Kyoto protocol. However, recent studies suggest that moving material away from incineration and into recycling is likely to be the more favourable treatment for materials when these treatments are assessed in terms of their global warming impacts. However, the greenhouse gas inventories of countries do not include the ‘embodied greenhouse gas emissions' of imports, so that countries which import primary materials will see no reduction in their greenhouse gas inventories if they recycle.
Two recent ECJ rulings could have an impact on the RDF markets. The ECJ (Case C-228/00) ruled that use of waste as a fuel in a cement kiln is recovery when excess heat is generated and that heat is used in the process In contrast, the ECJ decided in February 2003 (Case C-458/00) that burning waste in a municipal incinerator, whether or not it reclaimed energy, should be classified as waste disposal rather than recovery. The report, however, did not cover in details these aspects which took place at the final stage of the study and which assessment of effects would be a complex exercise.
It appears that waste and energy policies interact to make this a complex and a dynamic area. As such, it is difficult to make clear predictions as to what is likely to happen in future. What does seem clear, however, is that the current developments are accelerating the overlapping of energy and waste policies. Policies on waste management, greenhouse gases control and energy need thoughtful integration which takes account of the broader environmental implications. Also, flexibility is needed to accommodate continuing progress in minimisation, re-use and source separation for recycling/composting/anaerobic digestion.
One of the less expensive and well-established technologies to produce RDF from MSW is mechanical biological pre-treatment (MBT). An MBT plant separates out metals and inert materials, screens out organic fractions (for stabilisation using composting processes, either with or without a digestion phase), and separates out high-calorific fractions for RDF. RDF can also result from a ‘dry stabilisation process' in which residual waste (after separating out metals and inert materials) is dried through a composting process leaving the residual mass with a higher calorific value.
RDF production from MSW is most active in Member States with high levels of MSW source separation and recycling (i.e. Austria, Germany, Netherlands are the best examples), as the recycling activity generates non-recyclable high calorific residues suitable as RDF. The total quantities of RDF produced from MSW in the European Union have been estimated to amount to about 3 million tonnes. The capacity for RDF production from MSW is on the increase in Austria, Belgium, Finland, Italy and Netherlands with new MBT plants being built.
There is some limited co-incineration of RDF from MSW in Europe. RDF from processed MSW is reported to be incinerated in fluidised bed incinerators in the UK for energy generation, in multi-fuel district heating plants and paper mill boilers in Finland and in a few cement kilns in Austria, Belgium, Denmark, Italy and Netherlands. It is not always possible to secure an outlet for RDF and some quantities have to be stored. The total quantity of RDF coincinerated has been estimated to amount to about 70% of the quantities produced. The quantities of RDF burnt are expected to increase in the future mainly in Belgium, Italy and in the UK. There are also plans for using RDF from MSW in other non-combustion processes such as gasification and pyrolysis.
A wide range of industrial wastes are also processed to be co-incinerated in industrial processes as secondary fuels. These wastes include plastics and paper/card from commercial and industrial activities (i.e. packaging waste or rejects from manufacturing), waste tyres, biomass waste (i.e. straw, untreated waste wood, dried sewage sludge), waste textiles, residues from car dismantling operations (Automative shredder residues - ASR) and hazardous industrial wastes such as waste oils, industrial sludge, impregnated sawdust and spent solvents. These wastes need to have a high calorific value, to be consistent in quality and to be cheap or even support a gate fee. In the past few years, the market for substitute fuels has been very buoyant with the arrival of cheaper fuel substitutes such as meat and bone meal following the crises of BSE and dioxins.
Secondary fuels processed from industrial waste are commonly co-incinerated in cement kilns across Europe. About 105 kilns are reported to co-incinerate more than 2.5 million tpa of secondary fuels, mainly hazardous waste such as spent solvents, used oils and tyres. In the last two years, the cement industry in Austria, Belgium and France has also co-incinerated large quantities of meat and bone meal, estimated to amount to 350,000 tpa. Other industrial wastes (i.e. paper rejects, waste wood, dried sewage sludge, waste textiles and residues from car dismantling operations) are also co-incinerated in cement plants.
District heating plants and the power industry is another sector using industrial RDF in its coalfired power plants. They mainly co-combust non-hazardous secondary fuels such as waste wood, straw and dried sewage sludge. The co-firing of biomass waste in coal-fired power stations is likely to increase following the implementation of the EC Directive on Renewable Energy as it can account towards renewable obligations.
The paper industry also co-incinerated large quantities of waste mainly originating from its production processes (i.e. bark, paper sludge, spent liquor).
It is reported that most waste used in the iron industry are by-products of the process or waste recycled in-house in the sintering plant as reducing agent rather than energy substitution.
The assessment of the environmental impacts of the production and use of RDF has been undertaken using a multiple approach including:
- An LCA type system analysis that considers general benefits or disadvantages of the total recovery system of RDF;
- An EIA type estimation of local impacts of the production and use of RDF; and
- An assessment of impacts on the products from industries co-incinerating RDF.
The assessment compared the use of RDF in brown and hard coal power plants, cement plants and MSW incineration plants. The calculations were based on the assumptions that the materials (both RDF and fossil fuel) were of average quality and that the technology modelled for the installations was of average to advanced level (in respect to BAT) for production and utilisation of RDF. The specified standards in the model for MSW incinerator are ensuring compliance with the new Incineration Directive 2000/76 while this could not be guaranteed in this assessment for cement and power plants as emissions will be dependant on the specific waste type used as a secondary fuel and on the ratio of energy substitution for waste derived fuels. In the power plants, the co-incineration ratio was set at 5% of the thermal energy supply while the ratio in the cement plant amounted to 50%.
The LCA has focused on RDF processed from MSW, especially high calorific fractions from dry stabilisation and compared co-incineration in brown coal-fired power plants, hard coalfired power plants, in cement works with its incineration in MSW incinerators (MSWI).
The main conclusions of the LCA on the production and use of RDF are that none of the options is globally advantageous. On the one hand, due to the effective substitution of primary fossil fuels by RDF use in coal power plants and cement works, the co-incineration options show a large number of ecological advantages when they are compared with the alternative combustion in a MSWI. On the other hand, this general statement has, however, to be qualified by the tendency of industrial plants to cause higher emission rates (especially of mercury) than a modern MSWI. The benefit of using RDF as fossil fuel substitute at industrial plants must be secured by adequate controls on emissions and the quality of input materials.
Although the modelled scenarii in this assessment represent a high standard technology (BAT) there is potential for optimising equipments in both incineration and co-incineration plants which means that differences might scale down but the trends will not be reversed.
The simplified EIA of possible negative impacts on the surroundings of a plant burning RDF leads to similar conclusions. With the given assumptions of average to advanced technologies in the EU for power generation, cement works and MSWI, and typical conditions regarding chimney stack controls and climate, no severe environmental impacts will be observed at a local level. Nevertheless mercury at the cement works and cadmium at the brown coal-fired power plant are the weak points for the use of RDF even if they are still below a 2% threshold of air quality guidelines. Content of these heavy metals in RDF and flue gas cleaning systemsat the plants have to be managed to limit these potential negative impacts.
The most difficult part of the environmental assessment of co-incinerating RDF is connected with the potential impacts on the products and by-products. Five different secondary fuels were tested and compared with not using RDF; ASR (automotive shredder residue), paperreject pellets, demolition wood, RDF produced from Trockenstabilat and Nehlsen mechanical biological treatment (MBT) processes.
The results of the assessment showed a change in the toxic load of all products and byproducts (e.g. clinker from cement plants, gypsum, fly ash and slag from coal power plants). There was an increase in the content of contaminants such as chloride and metals e.g. lead, cadmium copper and zinc. The toxic loading depended on the type of RDF used - automotive shredder residues (ASR) produce a higher toxic loading than demolition wood or RDF from MSW. These effects are even more evident when co-incineration of RDF in taking place in brown coal power station as brown coal is less loaded with heavy metals than hard coal.
These materials are typically used or re-used in the construction industry so an increase in toxic loading is of concern for the environment and health (i.e. availability of chromium in cement). The study has, however, not looked at binding conditions, bioavailability or leaching of these contaminants. Slag and ashes from MSWI are often recovered and used as a secondary aggregate for road construction, although this has not been included in this analysis.
It is important to remember that the results of this assessment can vary if different assumptions than the ones presented above are used. The key parameters for which the sensitivity of the model is high are summarised below:
- The technical standard of the combustion plant is one of the most sensitive parameter. Setting rather low standards concerning MSWI as well as co-incineration plants would lead to a modified picture. But for plants that generally meet the targets given by the New Incineration Directive (for MSWI as for co-incineration) the differences are rather narrow.
- Another key parameter is the quality of the substituted fossil fuel. A low difference in burden of pollutants between conventional fuel and RDF strengthens the advantage of coincineration. To compare scenarii between “with and without RDF”, it is advised to define an average fossil fuel content of heavy metals and use it for benchmarking. It can be used for direct comparison of different types of RDF or even serve as basis for the development of a material specific standard. That standard could be defined as an average content of heavy metals in a product and have the regulations specify for example an enrichment factor not higher than 2.
- Also the energy efficiency of MSW incineration plant is a sensitive parameter. There are existing plants that deliver most of their processed energy for district heating. These plants have nearly the same high-energy effectiveness as power plants or cement kilns but have a more efficient flue gas cleaning equipment.
There are a number of factors which would seem to be favouring an increased use of RDF in co-incineration facilities. Whilst the economic drivers may be increasingly strong, they are somewhat complex and coupled with local conditions and policies such as the strategy chosen by Member States to implement the Landfill Directive and its obligation to divert large quantities of biodegradable material away from landfill within the next few years.
A range of cost factors influence the situation, including all of the major factors determining the costs of incineration, the costs and revenues associated with the output of RDF production plants, and the market for the calorific value produced in the process itself. Another factor which may enter the decision-making process is the geography of the country concerned. A dispersed population may make investment in smaller-scale facilities prohibitive, and this may tend to favour co-incineration where suitable industrial outlets already exist.
The decision for a municipality or waste management company to produce RDF through MBT or to rely on MSW incineration to comply with the Landfill Directive will depend on whether the costs of the MBT process are less than that of incineration or thermal treatment. Hence, though it is difficult to generalise, where the cost of incineration is low, the desirability of MBT will rest upon the ability to make use of RDF in a low cost manner. For example, the costs of conventional energy are high and/or the use of RDF requires no additional investment.
Where the cost of incineration is high and where source separation is well developed, the MBT route is still more favourable. This partly reflects the fact that moderate sized composting equipment (circa 20,000 tonnes) tends to cost half the cost of incineration. Indeed, it may become a cheaper option even where RDF is combusted in dedicated incinerators since the mass reduction achieved and the higher calorific value of the remaining material may ‘pay for' the separation and treatment process.
Local market conditions in addition to treatment process cost will influence the overall economics of RDF operation. For example, the gate fee for capital intense, ‘constant throughput' facilities such as incinerators, is not related to costs. Where these have excess capacity, the gate fee can fall significantly below costs and it is entirely possible that the lowest cost treatment of RDF may be its use in an incinerator.
There are additional reasons for a municipality to chose MBT as a more flexible solution to mass-burn incineration. Not only can the biological treatment aspect of the process be made modular (to allow switching away from treatment of mixed waste to composting of sourceseparated waste) but also the use of RDF in co-incineration plants removes the need to invest in capital intense, dedicated incineration (or thermal treatment) facilities.
Alternative management options
A number of studies about waste management alternatives show that from a system specific point of view, landfill is the least favourable option in terms of environmental impacts and efficient use of resources and that for each waste type, no net benefit can be obtained from the final disposal of that waste. As long as any kind of well managed recovery – ranging from recycling to energy recovery even reclamation of energy in a municipal incinerator – deliver environmental benefits, the lack of benefit from the landfill option clearly devalues the landfill alternative. In particular this type of assessment shows that high calorific value wastes are literally wasted when landfilled. Applying the landfill option for a possible RDF waste stream should only be considered for waste material for which the energy recovery might cause a high environmental impact.
A key concern is whether the manufacture of RDF is likely to jeopardise prospects for higher rates of recycling of materials. The MSW fraction used to produce RDF is generally the nonrecyclable residue left after sorting/recovery/recycling pre-treatment. However this is not always true. For example, if the waste collector is paid for the delivery of waste which can be used as fuel, and if this exceeds the material value which could be derived from material recycling, the use of material as fuel is likely to persist.
RDF from MSW can be utilised in other processes than incineration and combustion. Gasification and pyrolysis processes are generally promoted as “greener” alternatives to incineration or energy-from-waste. Via gasification, the energy content of the waste is transformed into a syngas which can be re-used as chemical feedstock or to produce power. Pyrolysis produces from waste a bio-fuel and syngas which again can be used as chemical and/or for power production. However, the major negative factor about adopting gasification and pyrolysis for waste treatment is that they are less proven in operation than mass burn incineration and can be just as inflexible as mass burn incineration. In contrast to mass burn incineration, which is optimised around large-scale single site implementation, many gasification and pyrolysis processes lend themselves to economic implementation at smaller scale.
An economic comparison is an essential part of any review process. However, this is not a straightforward issue on which it is easy to provide conclusions. “Real” cost data do not exist for many processes because they are at an early stage of development and, even where they do exist, the economics are very sensitive to site, local and regional factors, making direct comparison from a reference site to another specific project potentially misleading.
IV CONCLUSIONS AND RECOMMENDATIONS
- As long as any kind of well managed recovery – ranging from recycling to energy recovery even reclamation of energy in a MSW incinerator – deliver environmental benefits, the lack of benefit from the landfill option clearly devalues the landfill alternative for high calorific value wastes.
- Use of RDF in industrial processes offers more flexibility than incineration. It leaves more opportunity for future recycling programmes, it does not need to be fed with a constant amount of waste and it does not require investment in capital intensive dedicated incineration facilities.
- Use of RDF in coal power plants and cement works, due to the effective substitution of primary fossil fuels, shows a large number of ecological advantages when they are compared with the alternative combustion in a MSWI as long as the plants comply with the New Waste Incineration Directive 2000/76.
- However, mercury emissions might be problematic when RDF is co-incinerated in industrial processes and special measures should be developed (permits, amending 2000/76, and/or minimum quality standards for RDF).
- There is a need to study the increase of heavy metals in cement and other by-products from co-incineration facilities to investigate possible environmental consequences this maycause.
- Market mechanisms may favour inclusion in RDF of fractions that could be recycled in favourable environmental and economic conditions.
- This phenomenon could increase for some types of RDF (i.e. biomass waste) as a consequence of Directive 2001/77/EC on renewable sources of energy
- There are technologies other than combustion which can convert MSW into energy sources; gasification and pyrolysis. However, the major negative factor about adopting gasification and pyrolysis for waste treatment is that they are less proven in operation than mass burn incineration and can be just as inflexible.