This week Exeter City Futures is pleased to introduce work experience student Leo – our first Energy Explorer. Over the course of the week Leo will be exploring issues surrounding energy efficiency in the Exeter region and sharing his own experiences of commuting, renewable energy generation and making buildings more energy efficient. In this blog Leo explores the Exeter Energy Recovery Facility.
Recently I, along with team members from Exeter City Futures, participated in a tour of the Exeter Energy Recovery Facility. They incinerate waste in order to generate clean electricity which benefits Exeter.
What? Who? Where? When?
The facility was built on the site of an old incinerator which is located on the Marsh Barton industrial estate in Exeter, and has been operational since July 2014. It is a partnership between Devon County Council, Viridor, and Cyclerval (an offshoot of EDF who manage the plant).
Where does the waste come from?
The majority of waste comes from Exeter and the surrounding constituencies of Greater Exeter, including East Devon, Mid Devon, and Teignbridge. It takes our household waste that cannot be recycled; so anything that we put in our black wheelie bins.
Instead of dumping them in landfill, the collecting trucks take our waste during the fortnightly household collection to the facility’s waste bunker. This means that less waste ends up in landfill, therefore the job of managing its safe decay over hundreds of years becomes slightly easier.
If too much waste ends up in landfill, it could potentially pollute the land and infiltrate the water table and supply; causing significant environmental damage to the surrounding area.
How is it incinerated?
Firstly, the waste is continuously mixed in the bunker by a large hydraulic claw, which periodically transfers some into the feeding hopper.
The furnace has an oscillating kiln element which ensures that all the waste is incinerated evenly. At this stage, the kiln has air injected into it to promote waste combustion and control the temperature at about 850°C!
What is produced?
Bottom ash is one of the products of incineration, which is not hazardous and can be disposed of safely in landfill. However, the ash from the Exeter plant does not go to landfill. It is bulked along with the ferrous metals and sent to be processed into a secondary aggregate. Any unburnt metal that contains iron is removed by an electromagnet and recycled.
The others are a collection of gases that are produced by the combustion of waste, which include carbon dioxide. The gases are separated first and some are purified and converted into harmless nitrogen by the addition of urea. Chemicals, such as quick lime and active carbon, are also added to remove acidic metals and pollutants.
Air Pollution Control (APC) gases that contain carbon are further converted into aggregate – which is used to make concrete blocks in new houses and buildings, such as the Shard! APC residue is also a physical product, which is sent to Carbon8 for processing. More information on this process can be found on their website.
These processes may seem lengthy, but are in fact a good form of emissions control, as the plant releases few greenhouse gases.
So how is electricity generated?
As for the electricity generation system, the waste heat from burning rubbish in the furnace is used to turn water into high pressure steam. Here, the water is contained in a large network of pipes in the boiler to increase the surface area available for the heat energy to give the steam kinetic energy.
The steam is transported through the pipes to then drive a turbine by converting kinetic energy into useful electrical energy. The Exeter ERF’s oscillating kiln technology is unique in Devon, although there is a similar facility in Plymouth but with different furnace technology, and the steam produced generates 3.5MW of electricity – which is enough to supply around 5,000 homes!
Are there any challenges?
The Energy Recovery Facility also has the potential to run an additional district heating scheme within Exeter. This would give further benefits to the local economy by re-using waste heat energy from other locations, and supply up to 13MW of hot water to others!
However, there is currently no infrastructure that would link these sites up so that they could transport their waste heat between themselves efficiently.
Why is it ‘green’ energy?
This is because the energy from the waste is ‘recovered’ by incinerating waste that would otherwise end up in landfill. If the facility produces too much energy output, then it is sold back to the national grid and can be used by anyone around the country. The process that occurs at Carbon8 is also green because it is carbon negative.
I found the tour very interesting, particularly as it allowed me to see where our waste goes and the generation process of a renewable energy source in action.
At Exeter City Futures, we support the generation of electricity like this because it not only produces clean, environmentally-friendly energy, but also provides an alternative waste disposal solution; thus killing two birds with one stone!
If you want to become an Energy Explorer like Leo share your experiences with us on Twitter @ExeCityFutures or on our Facebook page. Let us know how much energy you’re using, and how you’re making your lifestyle more energy efficient.