بهینه سازی استفاده از پسماند در سیستم انرژی آینده Optimization of use of waste in the future energy system

abstract Alternative uses of waste for energy production become increasingly interesting when considered from two perspectives, that of waste management and the energy system perspective. This paper presents the results of an enquiry into the use of waste in a future energy system. The analysis was performed using the energy system analysis model, Balmorel. The study is focused on Germany and the Nordic countries and demonstrates the optimization of both investments and production within the energy systems. The results present cost optimization excluding taxation concerning the use of waste for energy production in Denmark in a 2025 scenario with 48% renewable energy. Investments in a range of waste conversion technologies are facilitated, including waste incineration, co-combustion with coal, anaerobic digestion, and gasification. The most economically feasible solutions are found to be incineration of mixed waste, anaerobic digestion of organic waste, and gasification of part of the potential RDF (refuse derived fuel) for CHP (combined heat and power) production, while the remaining part is co-combusted with coal. Cocombustion mainly takes place in new coal-fired power plants, allowing investments to increase in comparison with a situation where only investments in waste incineration are allowed.
۲۰۱۱ Elsevier Ltd. All rights reserved. 1. Introduction Use of waste for energy production becomes increasingly interesting, seen from an environmental as well as from the point of view of an energy system. When regarding waste as an environmental problem, a number of issues are important. First of all, waste amounts are increasing and so increasing amounts need to be treated [1]. Secondly, by 2014 the EU wishes to reduce the amount of landfilled biodegradable waste to a maximum corresponding to 35% of the biodegradable waste produced in 1995 [2]. Finally, the EU now accepts energy-efficient waste incineration as recovery, whereby it moves up the ladder of the waste hierarchy. The waste hierarchy prioritizes waste treatment in the following order from the top-down: waste prevention, re-use, recycling, recovery and safe disposal as a last resort [3]. Seen from an energy system perspective, it is interesting to include more organic waste in the energy system as this will increase the level of renewable energy in the system and hence decrease CO2 emissions. In this way, including waste in the energy system becomes instrumental in achieving the goals of 20% renewable energy and 20% lower CO2 emissions set by the EU for the year 2020[4]. Furthermore, if waste is used to produce bio-fuel for transport this could contribute to the EU goal of having 10% of the transport sector supplied with sustainable fuels by 2020. Compared to other countries, a very high proportion of the waste produced in Denmark is utilized for energy purposes i.e. 23%, and only 6% is landfilled [5]. There is, however, a lack of waste incineration capacity in the Danish system and old plants need replacement [6]. Currently, up to 20% of the electricity consumption in Denmark comes from wind power. Waste incineration has difficulties coping with the demand for flexible power production arising with increased shares of fluctuating wind power production. Waste is difficult to store and the plants have high investment costs which is why, preferably, they should run full time. Currently, in Denmark, waste incineration produces combined heat and power (CHP) with low electrical and high heat efficiencies, covering 4% of the electricity demand and 20% of the district heat production. All year round this heat is used in the district heating networks with first priority. However, heat produced from waste is still cooled off in cooling towers, particularly during summertime [7]. Due to the increased focus on reducing heat consumption in houses [4,8] even more heat may be cooled off in the future, unless the waste is used otherwise. Alternative uses of waste for energy production may potentially improve the energy efficiency and enable augmented shares of wind energy in the system by increasing the flexibility, e.g. through the production of bio-fuels from waste