Waste-to-energy refers to processes that extract the residual energy from any sort of waste and convert it either into heat or ultimately electricity. It is estimated that if the U.S. reduced landfill by 65% and converted that into energy, it could provide 2% of the nation's electricity. It would also reduce the emission of green house gasses.
The Waste Hierarchy
Waste-to-energy sits almost at the bottom of the waste hierarchy.This hierarchy shows the different stages of waste, helping to minimize waste ending up in landfill, which is both energetically and economically ineffective.
Before waste is collected and managed by municipalities, waste should be avoided (e.g. supermarkets stop packaging vegetables). If it can't be avoided, waste should be reduced (e.g. size of packaging). Once it's been produced, it may be re-used. For instance, plastic carrier bags. Another example would be up-cycling in fashion where leftovers from manufacturies are sewn together to create new clothes.
Once products are no longer used and disposed of by the consumer, they become waste and enter a waste management cycle of recycling and recovery (waste-to-energy). Ideally, only waste that cannot be recylced or converted into energy should end up on landfill.
Waste that has been delivered by trucks will be sorted, automatically as well as manually, as some types of waste may require pre-treatment.
In the gas plant, the waste is heated, but not necessarily burnt, and converted into a high-calorifc gas. Here, oxygen may be added.
The gas is buffered in tanks to ensure all-time availability, and can be delivered to the gas turbine as needed.
There are 2,200 waste incineration plants worldwide, consuming 225 million tons of waste per annum. It is estimated that by 2017 between 52 - 75 million tons of waste capacity will be added. Europe will invest €17.8bn over the next 5 years, similar to China.
The biggest market is Europe, though the commissioning of new capacity will diminish by 2017, once the UK has caught up with the trend. In the UK, more than 65% of waste still go into landfill (see diagram to the right). Outside Europe, China will build the most, as there is currently 100% landfill. In some countries such as Denmark or Singapore, the amount of waste being finally disposed, is well less than 10%.