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Waste Becomes an Energy Resource

by B Hofer, Sulzer Infra and U Gautschi, SR aviReal, Switzerland

INTRODUCTION

Wooden packaging, non-recyclable waste paper and cardboard are only useless waste as long as their energy potential remains unused. By burning waste materials without pollution, "Papyron" turns them into an energy resource.

Papyron is the name of a trend-setting plant which produces electricity, heat and cold from renewable energy for the headquarters of Swissair in Zurich-Kloten. The small-scale combined heat and power station, operational since in March 1997, substitutes around 800 tonnes of fuel oil per year and, by CO2-neutral combustion, contributes to reducing the greenhouse problem. The return on investment of this eco-compatible energy system is about 24%, surpassing the already high commercial efficiency of 20% demanded by Swissair for such installations.

TOMORROW'S FUEL

"Waste isn't waste but renewable energy", emphasises Swissair's spokesman for energy and environment projects. Without doubt, the environmentally-compatible utilisation of the continually increasing amounts of waste occurring world-wide is of major importance.

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Waste turned into an energy resource: briquettes used by the Papyron plant

Of particular interest are the cellulose-based substances such as paper, cardboard and wood, which can be burned CO2-neutrally and highly efficiently to produce electricity, heat and cooling. Newspapers account for about one third of the waste cellulose. The enormous amounts of packing materials which accumulate especially in carrier operations and industry are also important energy sources.

PAPYRON

It was the tightening of the Clean Air Act in Canton Zurich in 1995 which made necessary the redevelopment of the heating and power station at the Swissair headquarters. The 20-year-old oil-fired heating system could have been replaced by a new model of the same type, capable of satisfying the new, lower pollutant limits (eg 80 mg NOx/m3). So what prompted the company to decide in favour of a plant costing almost three times as much, requiring investments of some CHF 10 million (CHF 2.5 million being for the renewal of existing installation parts), where CHF is the Swiss franc? Astonishingly, Swissair found that Papyron offers both a better environmental profile and higher commercial efficiency.

These two, often irreconcilable, requirements could both be satisfied because the company produces around 4,500 tonnes of waste resource materials yearly. Instead of creating disposal costs, these materials are used as fuel for Papyron and replace some 800 tonnes of fuel oil. Moreover, the electrical energy produced by the combined heat and power generation reduces the amount of bought-in power by more than 50%. It is these cost reductions and income from the sale of surplus heat which render possible the high return on investment of 24% and permit the extra investment for the environment-friendly plant.

ENERGY CONCEPT

Papyron's high overall efficiency (64%) results from the fact that it will operate at full output throughout the year. This constant utilisation rate for 8,000 operating hours per year is only possible because during the summer, when only water heating is required, the absorption system can produce cooling for ambient air conditioning and for electronic data processing operations. In winter, the existing heat pump supplies extra thermal energy. The energy flows are shown in detail in the energy graph. The generated heat serves not only the company's buildings but also 420 apartments and the nearby Hotel Mövenpick.

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Simplified schematic of the Papyron energy system

WASTE DISPOSAL

Waste incinerators in general must be capable of burning all kinds of refuse: kitchen waste, plastics, paper, wood, chemicals etc, and the combustion and filter technology is accordingly costly. Papyron, on the other hand, utilises only the separately collected substances: waste paper, cardboard and wood. Also possible is the use of energy grass (eg China reed), old timber and polyethylene. A standard waste incinerator is clearly over-qualified for these natural or quasi-natural substances alone.

Moreover, the end products of the new energy system are less environmentally hazardous and hence easier to dispose of. They consist of 95% ash, which can, for example, be used as an additive in the cement industry. Only 5% of the ash is captured in the catalyser and filter and has to be disposed of as hazardous waste.

The utilisation of renewable energy sources and the simple disposal of the combustion products makes Papyron an energy system of the future.

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Heat/cold production and power generation plotted as a function fo season

AN INTEGRATED SOLUTION

Non-recyclable paper, cardboard and wood are collected in a decentralised fashion in the operational buildings and on the airport terrain in press containers. From there they are taken by truck to the loading silo, after which they are processed into briquettes.

The multi-stage incineration process with degassing, burning-off of the low temperature carbonisation gases and subsequent waste gas cleaning guarantee minimal pollutant emissions. The catalytic converter reduces the yield of nitrogen oxides (NOx) to around 40 mg/m3, which is even lower than the values achievable by modern 'low NOx' firing for oil and natural gas.

A constant power output of 300 kW is generated by the small-scale combined heat and power station. The waste heat from the steam engine is used for heat production (winter) and for cooling (summer). If the waste heat from the combined heat and power generation is insufficient, the existing heat pump is also brought on line. Peak loads are covered with oil-fired boilers.

Sulzer Energy Consulting Ltd supplied the energy concept for this project and designed the heating, refrigeration and steam installations. Swissair has all the know-how necessary for further applications of this energy system.

For more information contact the CADDET Swiss National Team in Aarau.

The CADDET Renewable Energy Newsletter is a quarterly magazine published by the CADDET Centre for Renewable Energy at ETSU, UK.

The articles published in the Newsletter reflect the opinions of the authors. They do not necessarily reflect the official view of CADDET.

Enquiries concerning the Newsletter should be addressed to
Pauline Toole, Editor, CADDET Centre for Renewable Energy, ETSU, Harwell, Oxfordshire OX11 0RA, United Kingdom. Tel: +44 1235 432968, Fax: +44 1235 433595.