Cooling from heat
The energy efficiency of waste incineration plants has become more important than ever. The production of cooling from heat has now provided an additional reason.
When operators talk about the merits of their waste incineration plants they often like to mention the disposal reliability they guarantee for the particular areas they serve. They can always be relied upon, both in summer and winter. That is one aspect of their work: the other one is unrelated to the pure disposal of waste. And that is when they often start to speak of electricity and district heating.
By Stephan Peter Krafzik
"The main thing is to exploit the energy contained in the waste as efficiently as possible," says Carsten Stäblein, Chairman of the Board of the major German waste disposal company E.ON Energy From Waste. That sounds good but is not so simple to implement in practical terms. Waste incineration plants require a sufficient number of connections per square kilometre in the heating network to make provision financially viable. Furthermore, fluctuating heating requirements also have to be taken into account: district heat is mainly required in the cold months of the year, but in the summer demand falls drastically.
"The relationship between the need for district heating in winter and in summer is highly disproportionate," emphasised Norbert Tanner from the waste-to-energy plant in Kassel, Germany. The essential thing is to bridge the "thermal summer gap" as efficiently as possible.
The waste incineration plant in Vienna was designed by Friedrich Hundertwasser.
An increasing number of plant operators have meanwhile found an answer to this problem. In summer they make use of the resulting heat to produce energy for cooling purposes. Cooling that is used to air condition the interiors of various facilities. The waste incineration plant in Göppingen, for example, supplies the local clinic with cooling and in Kassel both the city hall and a shopping centre are being supplied. "Cold exchangers are the market of the future," enthused Ferdinand Kleppmann, President of the "Interessengemeinschaft der Thermischen Abfallbehandlungsanlagen in Deutschland" (ITAD), the association of thermal waste treatment plants in Germany.
The subject could also be of interest for countries in Southern Europe. Countries such as Spain or Greece have comparatively long periods of high temperatures and their need for heating is thus limited. What they actually need is power for cooling. Its production could become a major criterion when they have to invest in new waste treatment plants in future and need to decide between waste incineration plants and those specially designed for mechanical-biological waste treatment.
Reliable figures not yet available
In Germany the subject was only discussed among a small circle of experts for a long time, but meanwhile a far greater number of those from industry have started to become interested. In September the ITAD made the provision of district cooling the main topic of its climate and resources conference in Würzburg, Southern Germany. It is not yet clear as to how many waste incineration plants in Germany already convert heat into power for cooling purposes. Reliable figures are not yet available and the market is currently in the process of developing.
Germany's neighbours in Austria are already quite a bit more advanced. In Vienna, for example, one quarter of the city's district cooling requirement is already being covered by waste incineration. The district cooling network is to be further expanded between now and the year 2030, according to the plans of the city's councillors.
Whereas in Germany the generation of cooling is decentralised, in Vienna it is quite the opposite. The consumers are office complexes that need to be air conditioned as well as hospitals or universities. The total consumer requirement is estimated at almost 200 megawatts of district cooling. Approximately one quarter of this amount could be supplied by the waste incineration plant in Spittelau, Vienna.
Cooling needs in Europe will grow continually, forecasts Alexander Wallisch from the Austrian district heating specialist Fernwärme Wien GmbH. The provision of district cooling is a service that satisfies the growing demand for convenience and a reaction to the increasing length of periods of warm weather. In Austria the demand for electricity in summer has already grown by eight per cent.
Developments in Germany indicate a similar trend. Cooling is principally needed in industry and accounts for approximately half of the consumption. A further 40 per cent is accounted for by public buildings, hospitals and shopping centres.
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