Waste Management: Energy Recovery from Solid Waste

Transcription

1 8 th International Symposium Topical Problems in the Field of Electrical and Power Engineering Pärnu, Estonia, January 11-16, 2010 Waste Management: Energy Recovery from Solid Waste Genrietta Jõgi AS Kunda Nordic Cement Viktoria Bashkite Tallinn University of Technology Tatjana Karaulova Tallinn University of Technology Abstract A number of companies offer technologies to sort the waste. The objective is to recover as much paper, cardboard, metal, plastic and other recyclable products from the waste as possible. The recycled waste is then sold to manufacturers who recycle the waste into their manufacturing processes. The purpose of the front end processing is to prepare the waste into a more usable waste product called "Refuse Derived Fuel" or "RDF". AS Kunda Nordic Cement in Estonia today is the only company whose technology enables the process of simply prepared a large quantity of waste incineration plants. Solid waste energy for cement production is an opportunity for reuse of waste. Keywords Waste management, recycling, Waste to Energy, Refuse Derived Fue, 1 Introduction Waste collection, transport and disposal into a landfill are not waste management. Managing waste is the collection and ultimate disposal of the waste without causing environmental damage. Every city in the world accumulates significant waste and has to deal with the problem of how to dispose of it. The amount of municipal waste generated per person can vary from 2 pounds per day per person up to 5 pounds per day per person, depending on the country and level of affluence. This amount does not include hazardous waste, industrial waste and other types of waste what are not included in the definition of municipal waste. The waste should be managed and treated as a resource, not a liability, and the waste can be processed in an environmentally friendly manner that will eliminate the need of landfills in the future. What is the most important the valuable products can be recovered from the waste Growing waste volumes On average, each European citizen generated 460 kg municipal waste in This amount rose to 520 kg per person in 2004, and a further increase to 680 kg per person are projected by In total, this corresponds to an increase of almost 50 % in 25 years [1]. Fig. 1. Generation and management of municipal waste in Europe EU15 - Austria, Belgium, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, Netherlands, Portugal, Spain, Sweden and the United Kingdom. EU12 - Bulgaria, Czech Republic, Cyprus, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Romania, Slovenia and Slovak Republic. This projected continuous increase in waste volumes is caused primarily by sustained growth in private final consumption (i.e. an average growth in the EU 15 and EU 12 respectively of 2 % and 4 % per year by 2020 (EC, 2006)) and a continuation of current trends in consumption patterns. These results indicate that the efforts to prevent the generation of waste should be significantly reinforced Increasing recovery and diversion of waste from landfill Historically, disposal by dumping has been the predominant treatment method for municipal waste, but over the last two decades considerable reductions in dumping have taken place. 250

2 In 2004, 47 % of total EU municipal waste was dumped on landfill. According to plan, it is expected to decrease further to around 35 % by Recycling and other recovery operations are expected to increase from the current level of 36 % to around 42 % by Finally incineration was used for 17 % of municipal waste in 2004 and is likely to increase to about 25 % by 2020 [1]. policy cannot be effective and can even lead to unintended effects (e.g. illegal dumping and export of untreated waste) [6]. 1.3 Waste in Estonia Estonia, as most of the Central- and Eastern European Country's inherited the dumping into landfills based on waste management system. There were ca 350 landfills (actually dumping sites without any environmental measures taken) very often in abandoned sandy gravel pits. In fact, for a long time there was no proper control of the waste types or amounts taken to the landfills. The Estonian landfills are filled up with different kinds of wastes. After bio-degradable waste, what is containing in household and similar non-hazardous waste, there are dumped also quiet huge quantities of wooden waste (saw dust, wood park etc.), sewage sludge, even major part of 'green park waste', waste tyres, different liquid waste, untreated medical waste etc. The Content of Bio-degradable (BD) waste in Municipal waste in 2005 is next [2]: Kitchen waste 43 % Paper, cardboard (incl. Packages) 28 % Garden waste 18 % Wood 5 % Others 6 % On 2005 there were generated ca tons BD municipal waste, from that tons (81 %) were dumped on landfills. Next aims of reduction of dumping on landfills were set (i.e 'diverting away from landfills' of BD Municipal waste [3]): t (8 % from dumped in 2005) t (38 % from dumped in 2005) t (61 % from dumped in 2005) Fig. 2. A simplified sketch of waste management system and the objectives of landfill Policy [6]. Note: GDP Gross Domestic Product; MBT Mechanical-biological treatment; RDF Refuse-derived fuel. 3 Extracting Energy from Waste Energy from waste (EfW) facilities combust waste under controlled conditions, to reduce its volume and hazardousness, and to generate electricity and/or heat. Waste hierarchy consists of 3 different levels (figure 3). 1. Prevention or reduction of waste production; 2. Recovery of waste (reuse, recycling, energy recovery); 3. Disposal of waste. The "Waste to Energy" (WTE) facilities include the following technologies [4]: It is expected that the residual waste will be incinerated in Estonia (ca 220 t/y) by For sure, it will influence the price of dumping, as dumping on landfills will decrease rapidly (+ efforts to develop source separation etc. recovery operations). 2 Structure of waste management system A policy for diverting waste from landfills can fully succeed only if the waste management system is able to receive and manage the waste flows. In particular, the 'maturity' of the system, i.e. the existence of separate collection schemes and recovery capacity, and its responsiveness to landfill diversion policy, can impact the effectiveness and the time frame of landfill policy. If the system is not ready to manage the diverted waste flows, landfill Fig. 3. Levels of waste hierarchy Mass Burn (MB) "Waste to Energy" plants generate electricity and/or steam from waste by feeding mixed municipal waste into large furnaces dedicated solely to burning trash and producing power. 251

3 Refuse-derived fuel (RDF) "Waste to Energy" plants remove recyclable or incombustible s and shred or process the remaining trash into a uniform fuel. A dedicated combustor, or furnace, may be located on-site to burn the fuel and generate power; or the RDF may be transported off site in order to use it as a fuel for boilers that burn other fossil fuel. The "Waste to Energy" facilities are Modular "Waste to Energy" plants, which are similar to Mass Burn plants, but there are smaller mobile units that may be quickly assembled where needed. 3.1 Recovered Energy System The Recovered Energy System recycles all the waste processed and converts 100% of it into energy and other products. Thus, this system is the ultimate recycling system. Best of all, the products recycled by this method require no sorting. Some WTE facilities cannot handle raw municipal waste and they require a sorting process on the front end of the WTE facility. The purpose of the front end processing is to prepare the waste into a more usable waste product called "Refuse Derived Fuel" or "RDF". Incineration capacity has increased in Germany and the Flemish Region to around 35 % of municipal waste generated. This is significantly more than in Finland (less than 3 %), Hungary (9 %) and Italy (16 %). It implies that a considerable part of waste diversion from landfills in Germany and the Flemish Region is due to waste incineration [6]. Estonia and Finland are now planning to make greater use of incineration with energy recovery. Both countries are situated in colder parts of Europe but whereas Estonia is seeking to reduce the use of oil shale for energy generation, Finland sees an opportunity to connect new waste incinerators to paper mills with stable energy demand throughout the year. Composting or anaerobic digestion is used to recover collected biowaste separately from households (kitchen and garden waste) and businesses, often together with comparable waste from the food industry. Mechanical-biological treatment (MBT) is usually used to treat mixed municipal waste. Materials suited for incineration or recycling are separated and biological treatment is then used to reduce the volume and organic content of the remaining fraction. The quality of the biologically treated waste fraction is usually poor and therefore it is landfilled or used as low-quality compost, e.g. as landfill cover. 3.2 Wastes to Energy Typical plant performance of "Waste to Energy" Combustion plants is as follows [4]: Combustion temperatures can be as high as 1100 C with high combustion efficiency and CO emissions of 15 to 40 ppm. Waste VOLUME reduction of 90%, depending on the type of waste. The amount of ash on a WEIGHT basis is as high as 25% of the input. The ash from earlier plants was considered to be toxic and required disposal in a landfill. However, with higher operating temperatures the ash is generally considered non-hazardous for all plants that have made the environmental changes. A small portion (<4%) of the ash is used in roadbeds and for other uses, however, the vast majority has to be disposed of in a landfill. To optimize the Waste-to-Energy process not only invest heavily in sophisticated filtering devices to minimise the emissions into the atmosphere, but also in increasing the energy efficiency of the plant so that it can generate as much sustainable energy from the waste as possible. On the basis, about 65 million tones (Figure 6) of household and similar waste, that remains after waste prevention, reuse and recycle, was treated in Waste-to-Energy Plants across Europe in billion kwh of electricity and 65 billion kwh of heat can be generated with these amounts of waste. Then 6-35 million tonnes of fossil fuels (gas, oil, hard coal and lignite) can be replaced. Replacing these fossil fuels, Waste-to-Energy Plants can supply annually about 12 million inhabitants with electricity and 11 million inhabitants with heat. This is equivalent to the entire population of Denmark, Ireland and Latvia what can be supplied with electricity. In addition, the entire population of Finland, Luxembourg and Slovakia can be supplied with the heat from Waste-to-Energy Plants throughout the year [5]. Plants incinerating waste had to comply with the Waste Incineration Directive and its strict emission standards. The extra cost of meeting these requirements made the use of Refuse Derived Fuel (RDF) unattractive for co incineration plants. 4 Combustible solid wastes reuse in Kunda Nordic Cement AS AS Kunda Nordic Tsement was established in 1992 and belongs now to HeidelbergCement Group. Today AS Kunda Nordic is a modern Estonian company offering constructional cements, crushed limestone and port services to customers from Estonia and abroad. From 1993 to 2000, cement production in Kunda underwent thorough renovation. One of the last implementation on AS KNC was solution to reduce fossil fuels in the cement industry, and at the same time to reduce the environmental impacts associated with the use of fuels. The s used in this article are opened and can be easily found [7], [8]. Although fossil fuels are principal energy sources, it is necessary to increase the use of alternative fuels derived from waste. From 2009 AS KNC will be able to use RDF (Refuse Derived Fuel), of which 252

4 Fig. 4. Waste-to-Energy Cycle (CEWEP, 2008) percent is made up of biomass. By replacing non-renewable fuels with alternative energy sources, it is possible to preserve natural resources and decrease fossil fuels CO 2 emissions. The cement plant in Kunda began to use the alternative fuels in Initially, different liquid residual products were used, such as waste oil, waste from the oil shale chemical industry and benzoic acid residue. In 2007, more than 36,000 tons of liquid waste fuels were burned in rotary kilns, providing about 10 percent of energy requirements, thereby reaching our target. In the future, it is expected that 85,000 tons of waste will be used as fuel each year. At maintained production levels, this would save 140,000 tons of oil shale each year and decrease greenhouse gas emissions by 5 percent. The proportion of waste for cement production is expected to increase in use of new technological line approximately by 35% of the total amount of the required fuel. The project aims the sustainable use of energy resources and the promotion of waste recovery and reduction of environment pollution loads. In particular, the desire to reduce emissions of packaging, automotive and electrical and electronic equipment waste in landfills. Project activities: the design of technological solutions; acquisition of equipment, building infrastructures; determine the suitability of the test run of technology; Analysis of the quantities of waste fuel and resource definition, negotiation with suppliers of waste. 4.1 Opportunities and challenges by using alternative fuels Since cement kilns require high temperatures, they are ideal for the combustion of alternative fuels especially residual products. Alternative fuels can also entail challenges. Since fuels vary in type and quality, technical solutions are also different and needed the confirmation, control and feeding. The supply requires proximity to urban centres where residue is produced. Future key challenges include identifying new bio fuels and collaborating with society to find solutions that minimise transport. With some stakeholders sceptical about the use of hazardous waste, openness is crucial. In general, the new installation for dosing RDF to kiln is controlled by distributed control system. Before incineration the waste must be pre-processed: sorted, dried, pressed, etc. In figure 5 is introduced layout of waste preparation for RDF. Fig. 5. Layout of the RDF system 4.2 Main elements of the RDF system Today's plant for the conversion of biomass fuel into energy should be designed to meet the stringent technical, environmental and financial demands of tomorrow. The Push Floor (Saxlund International Group) is designed to function with non free-flowing and difficult to handle bulk solid s. The push floor is moved back and forth on the base of the hopper by means of a double-acting hydraulic cylinder, driven by a hydraulic unit (figure 6). Consequently, the push floor activates the ensiled product such that, during each movement, is conveyed continuously into the opening provided in 253

5 the base of the hopper, under which a discharge worm conveyor may be arranged. certain distance, depending on the conveying. Pfister (Figure 10) Fuels are fed by a pre-feeding system via diverter flap to pre-hopper. The Weighfeeders TRW-S/D, provide high precision dosing. The fuels are fed via rotary valve into pneumatic transport line to mane burner or calciner burner. Fig. 6. Saxlund Push Floor Screw Conveyors (Figure 7). The product is conveyed from the draw-in orifice to the outlet. In being so, it is pushed along inside the enclosed trough by the helical screw gear. The trough mould is adapted to the dimensions and shape of the product to be conveyed. Fig. 10. Pfister Fig. 7. Saxlund Screw Conveyor Chain conveyor. is a continuous operating machine within a bolted rectangular cross-section casing. Magnetic drum (Figure 8). Material is typically fed on to the surface of the drum by vibratory feeder or chute work. The magnet system holds ferrous metal to its surface allowing the non-magnetic to fall away from the drum. Ferrous metal held on the surface is carried by the revolving drum to a position where the magnet system ends and it then drops away from the drum. Material feeding into the pre-hoppers. The calibration pre-hopper above Rotor Weighfeeder works additionally as buffer. A helical stirrer keeps the fuel in motion and ensures a constant fuel flow to the TRW-S/D. The load inside the hopper is measured by load cells underneath the frame. The calibration pre-hopper above the Rotor Weighfeeder works additionally as buffer. A helical stirrer keeps the fuel in motion and ensures a constant fuel flow to the TRW-S/D. The load inside the hopper is measured by load cells underneath the frame. Inside view Rotor Weighfeeder (Figure 11). Inner part of the Rotor Weighfeeder is consisting of lower sealing plate with discharge opening, rotor wheel including bars and inner ring as well as outer ring. The very slow rotating rotor wheel guarantees an almost maintenance free system. Fig. 8. Saxlund Magnetic drum Disc screen classifier (Figure 9). Saxlund-disc screens are designed for bulk. They were used in the several industries. Robust, high operating efficiency and low maintenance; these important characteristics make disc screens economical and environmentally friendly. Fig. 9. Saxlund Disc screen classifier There are several shafts in a casing running one after the other. On these shafts the discs are fitted in a Fig. 11. Material transport in the Rotor Weighfeeder The bulk transported by the horizontal rotor wheel from the inlet to the outlet falls down at the discharge opening by gravity. Pneumatic fuel transport. Rotary valve feeds the into the pneumatic transport system. Clean transport air from the blower is blown through the blowing shoe. Part of transport air is used for cleaning the chambers of Rotary valve. The air loaded with fuel is transported directly into the burner flame. 254

6 Online calibration during operation. During online calibration the supply the pre-hopper is stopped. The static load cells underneath The TRW- S/D frame measure the loss in weight during the calibration period. This value is compared with the weighing data of the Rotor Weighfeeder TRW-S/D. If necessary the online taring can be executed. means the Weighfeeder is used in a wrong way and something has to be done in order to relieve the filling of Weighfeeder. Optimization of working load will help to get better result. The IDEF simulation model with the all functions is described in figure Functional model of the system In this research we attempt to simulate the RDF obtainment process from the solid waste with the aim to analyse and find the bottlenecks in this process. It helps us to find proper ways for implementation of fail-safe work of the whole system. In figure 12 is introduced diagram of the process by using IDEF0 method. Simulation of this diagram shows the productivity of system with RDF if we burn 5 tons per hour. The Resource States diagram shows the bottleneck in Weighfeeder. It Fig. 12. The RDF system elements loading Ma terial in hop per Material in Magnet Separator Material without metal pieces W aste (Garbage) A11 Charging and feeding of ma terial to feed-screw A12 Feeding of to the bottom tape and transportation A21 Removal of me tal pieces from A22 Removal of big pieces from Insufficient Needed Fuel mate rial (RDF) A33 Dosing of A32 Feeding and w eighing of A31 Cleaning of air (by filter) A23 Material delivery to filter Material in W eightfeeding Feeding of m aterial to the upper tape and transportation Classified Fig. 13. Simulation model of the RDF system functions 5 Conclusions The utilization of alternative fuels in cement kilns is becoming more and more common, since this is usually economically as well as environmentally favourable. Solution of a social waste problem through safe destruction of hazardous wastes; reduced greenhouse effect through replacement of fossil fuels by partly CO2 neutral fuels; cost reduction through replacement of more expensive fuels, such as coal, by alternative fuels. Waste-to-Energy is an alternative energy source that can help to achieve the EU s energy and climate targets for Granting the recovery status to WtE plants that generate energy based on Best Available Techniques will stimulate WtE plants to improve their energy efficiency. In order to divert waste from landfills, it is important that WtE plants are classified as energy recovery, i.e. higher up the hierarchy than landfilling. References 1. EEA Briefing ISSN Peeter Eek. Implementation of EU Landfill Directive in Estonia , Tallinn 2009 FEAD Seminar. 3. Peeter Eek. Organic waste legislation and consequences for the implementation, 2nd Baltic Biowaste Conference Recovered Energy, Inc. The Recovered Energy System 5. Confederation of European Waste-to-Energy Plants (CEWEP e.v.) Boulevard Clovis 12A I B Brussels I Belgium I 6. Diverting waste from landfill Effectiveness of waste-management policies in the European Union, EEA Report, No 7/2009, ISSN , European Environment Agency. 7. Saxlund International 8. Pfister FLSmidth 255