Feature Report: Waste Recovery

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Incineration - The Heating Power of Refuse

Incineration is not only a way to get rid of waste, it’s also a way of generating energy. Many different types of waste, whether from households, industry or agriculture, can be converted into heat or power.

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This waste incineration plant in Issy-les-Moulineaux, France produces enough heat for 5,000 homes in the western suburbs of Paris. © AFP

Harnessing Heat and Power Potential

Excluding all types of recyclingAny waste treatment process that uses materials from identical or similar end-of-life products or manufacturing waste to produce new products. , about 70% of our waste is combustible. That includes paper, cardboard, biodegradableA substance capable of being decomposed by naturally occurring fungi and microorganisms. waste, textiles, plastics and more. In addition to households, many industries produce waste whose value can be captured through incinerationTechnique used to convert waste into energy. The waste is burned, producing heat, power or both. . There are many kinds of industrial waste, including hydrocarbonOrganic compound consisting of carbon and hydrogen. Hydrocarbons are the principal constituents of crude oil, natural gas and petroleum products. residue, tar and used solvents. There are also various kinds of agricultural waste, such as straw from wheat, corn and rice, as well as agro-industrial waste, which mostly comes from sugar and oil mills. Papermaking creates waste, too. After extracting cellulose from wood to make pulp, pulp mills burn the by-product known as “black liquor.”

By exploiting its potential to recover energy from waste, Europe could provide 17 million homes with powerIn physics, power is the amount of energy supplied by a system per unit time. In simpler terms, power can be viewed as energy output... and 24 million with heatIn the field of statistical thermodynamics today, heat refers to the transfer of the thermal agitation of the particles making up matter... . Denmark is currently the European champion in terms of per capita power and heat production.

Incineration Plants

Incineration is first and foremost a way of eliminating a sizable amount of our waste. Some 90% of its initial volume goes up in smoke. This represents a healthier solution than the huge landfills of the past. In France, direct dumping of recyclable or recoverable waste has been prohibited since July 2002. In addition to getting rid of refuse, incineration allows us to produce energy from waste.

An incineration plant includes a furnace and a post-combustion chamber. The waste is burned in the furnace in a process called pyrolysisThermochemical decomposition of organic material at elevated temperatures... , which produces combustible gases. These are burned in the post-combustion chamber at temperatures of 800 to 900°C. A heat exchanger — in which very hot water or superheated steam circulates — is used to recover energy from the flue gas emitted.

70% of our waste is combustible

About 5 to 7 tons of waste is needed to produce the equivalent of one ton of fuelFuel is any solid, liquid or gaseous substance or material that can be combined with an oxidant... oil. For example, the energy produced in the three Paris-region incineration plants operated by Syctom is enough to heat 300,000 homes a year.

How Energy Efficient is Incineration?

Two types of energy are produced in an incineration plant: heat and power. Each type has its own production process and level of energy efficiencyIn economic terms, energy efficiency refers to the efforts made to reduce the energy consumption of a system... .

  • Heat production: This involves simply heating water through waste combustion. This process is energy efficient, with 70 to 80% of the combustion heat recovered after incineration, or about 1,500 kWh of thermal energy per ton of refuse. Of course, the heat produced then has to be used somewhere near the incineration plant (See the Feature Report: "Using Heat More Efficiently").
  • Power production: The heat exchanger has to contain steam at the highest possible pressure. This steam is sent to a turbine that drives an electric generator. The power produced can be supplied to the grid all year round. The energy efficiency of this process is about 20 to 25% (300 to 400 kWh).

A better solution to producing just heat or just power through incineration is producing both simultaneously through cogenerationThe simultaneous production of both heat (thermal energy) and power... , also known as combined heat and power (CHP). This involves using the residual heat in the exhaust steam from the power-generating turbine. With this process, energy efficiency improves to 50 to 60%.

In an incinerator, 5 to 7 tons of waste is needed to produce the equivalent of one ton of fuel oil.

It is estimated that by recovering 50% of all municipal waste in France, about 1% of the country’s energy consumption needs could be met. This solution is therefore very far from adequate.

Moreover, the flue gas from incinerating waste is highly toxic. The resulting gas must therefore be scrubbed and neutralized (because of its acidity) before being released. Air pollution around incineration plants is particularly high.