A long-time flame: Waste-to-energy still goes strong in Europe

The first use of waste combustion for energy recovery can be dated back over a hundred years in Europe. Today, waste-to-energy has developed into one of the most commonly used technologies for tackling Europe’s waste challenge, and efforts are ongoing to optimize its operation and widen its acceptance. by Edmund Fleck Waste-to-energy (WTE) is by no means a new technology. The first waste incineration plants were built in Europe in the middle of the 19th century to control ever increasing amounts of waste and to treat them in a hygienically safe way. By the beginning of the 20th century, volumes of waste were already substantial (Table 1) and not far removed from the 534 kg municipal solid waste (MSW) generated per person in the enlarged European Union (EU-25) in 2003.1 TABLE 1. Waste generated per person, 19092 City Weight (kg) Brussels 490 Budapest 250 London 302 Munich 230 New York 536 Zurich 227 Despite using a comparatively simple technology, the early plants soon practised the recovery of metals from residues and the use of bottom ash for construction. In addition, heat recovery boilers began to be used in the early 20th century to recover energy contained in the waste. Primarily due to financial constraints, widespread application of WTE technology did not occur until the 1950s. By this time, incineration technology had matured and continuous feeding of the waste and continuous removal of the residues were both standard practice. The main driver for using this technology remained the reduction of waste volumes in a hygienically safe way, especially in countries with limited space for landfilling, such as Japan or Switzerland. This is why some plants, especially in Japan, were of the ‘batch’ type, operating only during a limited number of hours per day. Waste-to-energy has gone a long way since the simple waste incineration in the mid-19th century Click here to enlarge image In the 1960s, concern about the environment became more important and prominent in Europe. More stringent regulations for the emission of pollutants to air first limited the emission of dust, and then the emission of acid gases (hydrogen chloride, hydrogen fluoride, sulphur dioxide, etc.) and heavy metals (especially mercury). Then in a third step, limits were placed on emissions of nitrogen oxides (NOx) and hazardous organic substances such as dioxins/furans (PCDDs/PCDFs). Mainly due to political reasons, emission limits for WTE plants in Europe were more stringent than for many other industrial processes (including coal-fired power plants, industrial combustion plants and metallurgical processes). In many cases, the technology needed to meet these requirements was not available and had to be developed by suppliers - often at considerable risk and cost. Today, EU emission limits for WTE plants remain the most stringent worldwide and the technologies are mature, safe and reliable. The role of WTE in Europe today Modern waste management consists of a number of steps making up what is often called the waste hierarchy. A recent Communication from the European Commission stated: Current EU policy is based on a concept known as the waste hierarchy. This means that, ideally, waste should be prevented and what cannot be prevented should be reused, recycled and recovered as much as feasible, with landfill being used as little as possible 3 In recent years, production of MSW has continued to increase in Europe by about 2% per year (Figure 1), and from 457 kg/person/year to 534 kg/person/year. As shown in Figure 2, the amount of MSW generated differs substantially between countries. FIGURE 1. Generation and treatment of municipal solid waste in EU-25, 1995-2003. source: eurostat1 Click here to enlarge image null FIGURE 2. Municipal waste generated per person in EU Member States, 1995 and 2003 (data is unavailable for some countries). source: eurostat1 Click here to enlarge image The amount of MSW landfilled in the EU-25 fell from about 64% in 1995 to around 49% in 2003. Originally landfills were simple dump sites, with the waste sometimes filling holes dug for some other purpose (e.g. strip mining). Today in Europe they are mainly controlled landfills, i.e. they have to be built according to strict requirements to prevent leachate penetrating the surrounding soil or underlying groundwater. Today’s stringent regulations have caused WTE plants to reduce their emissions dramatically via measures such as flue gas cleaning. photo: aeb Click here to enlarge image But landfills still require a large volume of land. They also generate odour. Loose fill materials can be carried away by the wind, and animals (rats, seagulls) populating landfills are a nuisance to people living in their neighbourhood. In addition, landfills need decades of observation after they are closed to check that no leachate escapes and collect the gases (mainly methane) generated by decomposition. Thus the risk of pollution over this long period of time is by no means negligible. And, last but not least, neither the energy contained in the waste nor valuable materials such as metals are being utilized. Considerable efforts have been made to recycle more MSW and to collect biodegradable waste separately and compost it. This effort (shown in Figure 1 as ‘Other treatment’) increased significantly from about 21% in 1995 to about 34% in 2003. But even so, a sizeable amount of waste remains that cannot be recycled and thus requires further treatment. This so-called ‘residual’ waste amounts in Germany to around 25 million tonnes per year - by no means a small quantity. Many European countries have now banned further use of landfills for disposal of residual MSW. WTE will increasingly work in conjunction with MBT, which provides high-calorific fractions for co-combustion. photo: amandus kahl gmbh & co.kg Click here to enlarge image As one alternative treatment method, mechanical- biological pretreatment (MBT) was introduced in some countries. For example, Germany has developed an annual MBT treatment capacity of 6-7 million tonnes. But pre-treatment still leaves about 50% of the original waste amount; it has a higher heating value than before but more or less the same energy and pollutant content. This fraction was thought to be usable for co-combustion in power plants or other industrial combustion plants. However, this market has not developed as expected due to increased risk of corrosion in the boilers of these plants and/or the necessity to comply with more stringent emission limits when utilizing this fraction. Gasification and pyrolysis: the reality For some time, pyrolysis and gasification of MSW was thought to be an alternative to ‘classical’ WTE technology, producing residues with ‘glass-like’ properties that aided recycling. But these processes have not been proven to work reliably under normal operating conditions. Furthermore the energy balance and economics do not currently support the use of this technology. This is true for Europe, where these technologies do not play a role anymore today - though they continue to be discussed, particularly in the UK. In Japan, some pyrolysis and gasification plants operate successfully, probably due to the different ‘quality’ of the MSW being treated. The remaining option This leaves only one available, reliable and, on a large-scale, proven technology, namely WTE. The percentage of MSW being incinerated in Europe rose from 14.9% in 1995 to 17.2% in 2003, an increase in capacity of about 10 million tonnes per year. According to the Confederation of European Waste to Energy Plants (CEWEP), there were about 409 WTE plants in Europe in 2003, with a total treatment capacity of some 47.7 million tonnes per year.4 The energy recovered could substitute for around 8.2 million tonnes of hard coal each year. This is essential both in terms of saving natural resources, but also in avoiding carbon dioxide (CO2) emissions which contribute to global warming. It has been generally agreed that 50%-60% of the residual MSW is biogenic in origin and so does not contribute to net CO2 emissions. A study made by the Öko-Institut eV in 2005 on behalf of the German Federal Environment Authority5 concluded that about 45 million tonnes CO2 equivalent could be saved between 1990 and 2020 by diverting residual MSW from landfills to WTE (a landfill ban came into force in Germany on 1 June 2005). This is a sizeable contribution to the mitigation of global warming. Some Member States now incinerate about 60% of their MSW (Figure 3) while others still rely heavily on landfill. The 10 new Member States currently have almost no WTE plants. Their current priorities are to draw up and implement appropriate waste management plans. These plans are likely to include the implementation of WTE plants as one important component in a sustainable waste management scheme. However, construction of these plants will take some years to actually commence. The fact that many of EU-15 Member States still rely heavily on landfilling suggests that Europe’s incineration capacity is likely to increase significantly in these countries in the next 10-20 years. FIGURE 3. Percentage recovery and disposal of municipal waste by country, 2002 (data is unavailable for some countries). source: eurostat1 Click here to enlarge image null A modern WTE plant Figure 4 shows a modern WTE plant. From the waste bunker, the waste is fed by crane to the feed chute. Controlled by the combustion control system, the waste feeder pushes a specified amount of waste onto the grate. FIGURE 4. A modern WTE plant. source: martin gmbh für umwelt- und energietechnik Click here to enlarge image The grate is usually divided into different zones along its length whose motion can be controlled independently. Combustion air is taken from the waste bunker and introduced underneath the grate, also via different zones which are individually controllable. This part of the combustion air (also called primary or underfire air) can be at ambient temperature or pre-heated using a steam pre-heater. Its function is first to dry the waste, then to incinerate it and finally to control proper burn-out of the remaining residue, slag or bottom ash. Bottom ash is removed by a wet discharger, while metals can be separated and recycled. The quality of the remaining material means it can be utilized, for example, in road construction. The flue gases from the grate still contain a certain amount of burnable components. Thus further combustion air, so-called ‘secondary air’, is introduced into the combustion chamber at some distance above the grate. Good mixing of the flue gas with this secondary air is essential to guarantee a proper burn-out of the flue gas and destruction of hazardous organic compounds. It is also important to complete chemical reactions as much as possible, thus helping to avoid corrosion in the subsequent evaporator section of the waste heat boiler. The combustion chamber is followed by the waste heat boiler, which recovers the energy released from the waste by generating steam. This boiler consists first of empty passes where the heat is transferred by radiation. This is followed by passes containing tube bundles, where the heat is transferred by convection. Various configurations of these heating surfaces are found in WTE plants. After the boiler, the flue gases pass through the flue gas treatment system, enabling the plant to meet required emission limits. The steam generated can be used: as process steam in industrial applications in a district heating network to generate electricity in a steam turbine/generator in a combination of the above. By far the most energy-efficient way is to use the steam for process or district heating purposes. However, this is not possible or appropriate in many cases - either for plants in warmer countries where no district heating is needed/installed or because the WTE plant is located too far away from potential users such that only electricity generation is possible. Corrosive compounds (chlorine, alkali metals, lead, zinc, etc.) in the waste mean that the corrosion potential in WTE plants is by no means negligible. As a result and for cost reasons, the steam temperature is typically limited to a maximum of 400°C. However, this renders the conversion to electricity less efficient than fossil-fuel-fired power plants. Even though WTE today can be considered a mature technology, improvements are still being made. For example, combustion control has been enhanced to secure even more stable operating conditions and to adapt better to changing waste properties. Various efforts have also been made to offer more ‘standardized’ WTE plants, largely to save costs. However, demand for such an approach has been slow. Outlook At the heart of many discussions today are issues such as sustainability, saving of resources, climate change and energy efficiency. WTE can make a contribution to all of these. Improvements to WTE technology have been and will continue to be made. photo: twence b.v. Click here to enlarge image An important aim is to increase the net amount of electrical energy fed into the power grid. Efforts are being made to reduce the internal electricity consumption of WTE plants. With that and optimization of the water/steam cycle, the net electrical efficiency can be increased from 20%-22% to 25%-27%.Using higher steam parameters, combined with additional measures to optimize the thermal cycle, can push the efficiency close to, or slightly above, 30%. Feeding the steam from the WTE plant into the cycle of, for example, a combined-cycle power plant can increase its efficiency to around 40%. However, the higher steam parameters pose a substantial risk for corrosion. This issue is the subject of intensive study and development, but is by no means solved - partly because the mechanisms leading to corrosion are not yet fully understood. In terms of flue gas cleaning, efforts are under way to further reduce combustion-related pollutants by so-called ‘primary measures’. This means reducing the quantity of pollutants generated in the first place or reducing them by adapting the combustion process. Work also looks set to continue in optimizing the utilization of residues from waste incineration. The actual rate of re-utilization depends on national or even local considerations, which encompass both economic arguments as well as more emotionally motivated issues such as the acceptance of any material originating from waste incineration. This brings us on to public support. A more positive attitude by the public toward WTE can be found in many countries and the benefits of WTE are slowly being recognized as outweighing its drawbacks. One objection to the use of WTE has been that it will jeopardize efforts to prevent and/or recycle waste. However, data on currently installed incineration capacity in Member States (see Figure 3) does not support this argument. For example, Denmark has both a high percentage of WTE and successful recycling schemes. Concluding remarks Although hygiene was originally the main concern, plant designers and operators are increasingly focusing on energy recovery. This new role is acknowledged in the proposed revision to the Waste Framework Directive published by the European Commission at the end of 2005.6 In this draft, WTE is - for the first time - recognized as ‘recovery’, alongside the underlying purpose of safely treating regulated waste. A criterion for energy efficiency is attached to this acceptance and ESWET is currently reviewing the placing of this criterion, the formula and the threshold value. To comment on this article or to see related features from our archive, go to www.waste-management-world.com and click the ‘Forum’ tab. Edmund Fleck is Chairman of ESWET (European Suppliers of Waste to Energy Technology) and a Managing Director of Martin GmbH für Umwelt- und Energietechnik in Munich, Germany.Fax: +49 89 35617 212e-mail: Edmund.Fleck@martingmbh.de Notes 1. EuroStat. Waste generated and treated in Europe: data 1995-2003, Office for Official Publications of the European Communities, 2005. 2. Etienne de Fodor, Elektrizität aus Kehricht. Budapest 1911. Published as facsimile edition by MABEG in 1989. 3. European Commission. Taking Sustainable Use of Resources Forward: A Thematic Strategy on the Prevention and Recycling of Waste. COM(2005)666 final, 21 December 2005. See http://europa.eu/scadplus/leg/en/lvb/l21197.htm 4. www.cewep.com 5. Öko-Institut e.V. Statusbericht zum Beitrag der Abfallwirtschaft zum Klimaschutz und mögliche Potentiale. Forschungsbericht 205 33 314 im Auftrag des Umweltbundesamtes, Öko-Institut e.V. unter Mitarbeit von ifeu-Heidelberg GmbH, August 2005. (in German only) 6. European Commission. Proposal for a Directive of the European Parliament and of the Council of 21 December 2005 on waste. COM(2005)667, 21 December 2005. See http://europa.eu/scadplus/leg/en/lvb/l21197.htm The WTE technology base is in Europe Three main components in a WTE plant must be adapted according to the characteristics of the fuel (waste) being incinerated: combustion system - the main component of which is the incineration grate. The system also includes the design of the combustion chamber and the combustion air system. waste heat boiler - in standard operation and maintenance, it is necessary to take account of fouling (where fly ash is deposited on the tubes in the boiler, thus reducing their effectiveness for heat transfer)and to protect the boiler from corrosion. flue gas treatment system. These components evolved largely in Europe: the core technology, the incineration grate, was developed chiefly by companies in Germany, Switzerland and, to a lesser extent, Belgium, Denmark and Italy. Europe has also led progress in developing new technology to recover energy in the waste heat boiler and to meet stricter emissions limits. Through licence or co-operation agreements, these technologies then found their way to other countries such as Japan, the US, Taiwan, China and Korea. Today, Europe is the most active market for WTE plants, both for new installations as well the replacement of existing facilities. It is expected to remain in this position for the foreseeable future. ESWET The European Suppliers of Waste to Energy Technology (ESWET) is the professional association of suppliers of components or complete WTE plants in Europe. Founded in 2004, today it is made up of 11 companies from five Member States (Austria, Belgium, Germany, Hungary and the Netherlands). Its main task is to represent suppliers at a European level, contributing their know-how to legislators in Brussels and elsewhere. By following European legislation and trends, ESWET can participate early on in all relevant discussions. ESWET is by no means against the waste hierarchy as described above. But it sees WTE as an important and integral part of a modern waste management scheme. Using the energy contained in the residual MSW and reusing some of the residues remaining after incineration is, in the opinion of ESWET, in line with the overriding goals of sustainability and resource conservation.