Turning Trash Into Energy

The city of Oslo in Norway has a problem the opposite of many other cities – not enough garbage.

Oslo has been burning trash to produce heat and electricity since 1967. Energy equivalent to around 840 gigawatt hours is generated annually from the city’s two plants.

The city sorts through around 410,000 tons of waste each year; diverting food waste to become biogas and bio fertilizer, plastic waste that is made into new plastic products and residual waste incinerated for district heat and electricity production.

For electricity generation, the heat from the incineration is used to generate steam to drive turbines. Around 160 GWh of electricity is produced at the two plants each year.

The district heating aspect heats water that is is pumped into a network of pipes. Houses connected to district heating have smaller pipes in their foundations, into which this heated water flows and produces equally distributed heat throughout the home above.

The city’s system works so well that Oslo is now having to import garbage to burn.

Modern waste-to-energy plants are quite efficient. There are strict controls on emissions and total conversion efficiencies upwards of 80% can be achieved.

So, soon we’ll be able to create as much garbage as we want; secure in the knowledge that it will be used somewhere else to create energy right?

Not really – it’s a low emissions process; but not zero emissions. A tonne of trash will generate around a tonne of carbon emissions when incinerated.

Aside from the all the resources and energy involved with making the items that then become trash, the trash also still has to get from the point of disposal to the plant.

As the NYT article linked to above points out, Oslo is now importing garbage from England, Ireland and Sweden. The country is also competing for garbage with other European nations as there are hundreds of waste-to-energy plants in the European Union.

That garbage has become a valuable item is a great thing as it means less goes to landfill; but that it’s being referred to as “renewable energy” is a little unsettling as it puts far too much of a green spin on it. We need to be reducing waste, not finding justification to generate more.

Still, it’s a fascinating topic and I think plants of this nature have a place in every major population center.

Waste to energy isn’t just incineration – there are all sorts of other processes already operating or being developed. These include gasification, thermal depolymerization, pyrolysis, plasma arc gasification, anaerobic digestion and fermentation.