TOWERING INFERNO: Reaches Sky-High Efficiency - Waste Management World
Again and again we hear the message that resources are scarce, and that we have to ensure that they are not lost in our waste. Explanations as to which resources we are talking about and how we avoid wasting them, however, are in short supply. Waste may contain many different resources depending on origin and prior use. The resources of waste may be considered a material resource, an energy resource or a nutrient resource, and typically a waste fraction will comprise a mixture of these in varying quantities. When evaluated from a materials and nutrients point of view, however, many waste fractions do not contain any significant recyclable resources without them first being subjected to thorough sorting and cleaning processes – processes which both economically and in terms of energy are very costly. At modern waste to energy facilities with combined heat and power production a highly efficient recovery of the most important resource of these waste fractions - energy - can be ensured.
TOWERING INFERNO: Reaches Sky-High Efficiency - Waste Management World
- 2. TOWERING INFERNO: Reaches Sky-High Efficiency - Waste Management World
- 3. • New political winds are blowing across Europe. The aim is resource efficiency but the means to this end are unclear. In the Energy Tower – a new waste to energy facility in Roskilde, Denmark - every effort is being put into maximising the recovery of the energy resource embedded in the waste.
- 4. • Again and again we hear the message that resources are scarce, and that we have to ensure that they are not lost in our waste. Explanations as to which resources we are talking about and how we avoid wasting them, however, are in short supply. • Waste may contain many different resources depending on origin and prior use. The resources of waste may be considered a material resource, an energy resource or a nutrient resource, and typically a waste fraction will comprise a mixture of these in varying quantities.
- 5. The Energy Tower • The utilisation of the energy resource of waste is the objective of a new facility, dubbed the Energy Tower, in Roskilde, Denmark. The design of the facility is focused on maximum utilisation of the energy resources in the waste, such that it may be harnessed with practically no losses.
- 7. • In the Energy Tower waste is utilised through conversion into energy in the form of electricity and district heating. The focus is on reaching the highest possible efficiency in order to avoid any loss of resources. The plant's waste treatment process produces heat in the boiler room which is used for the production of steam in the boiler. Through this process some 85% - 90% of the energy content of the waste is transformed into steam, and the steam is subsequently converted to electricity as well as district heating.
- 9. • The new €175 million Energy Tower is being built, financed, owned and operated by KARA/NOVEREN - an inter-municipal waste management company owned by nine municipalities west and south of Copenhagen. In addition to the Roskilde waste to energy facility, which includes three units from 1981, 1989 and 1999, the company operates 14 civic amenity sites, a recycling station, a landfill site for residual waste and two transfer stations.
- 10. Energy recovery and recycling in Parallel
- 11. • At the same time we have to increase the effort to maximise the recovery of energy from residual waste, which cannot be recycled in a sustainable manner. • Denmark has for many decades demonstrated that high recycling rates, even among the highest in the world, are compatible with waste to energy, and that with innovative thinking and dedicated effort both recycling and energy efficiency can be further increased in parallel.
- 12. • The high energy recovery efficiency in the Energy Tower is achieved by combining and integrating the design of the boiler with the flue gas treatment. During the incineration process, energy is extracted from the combustion by production of steam in the boiler while the temperature of the flue gas is decreased. • At the end of the boiler system the temperature is reduced to approximately 170°C. At this point, the flue gas is contaminated with dust and acidic components so further reduction of the temperature would cause operational problems with condensation of liquid acid. This would not only increase the corrosion of steel components, but also result in fouling on tubes etc. Therefore further energy recovery must be done after de-dusting of the flue gas and by equipment made of corrosion-proof materials.