15 steps from non-recyclable waste to energy – start the journey here
It all starts at home, school or in the workplace. That’s where the non-recyclable waste that arrives at the ERF is created. The next time you have something that you no longer want or need, let’s all play our part. Before you throw it in the rubbish bin, could you reuse or recycle it? By reducing waste and putting the right stuff in the right bin, we can make sure that only non-recyclable rubbish ends up at the ERF.
In the UK the waste hierarchy is used to rank waste treatment according to what is best for the environment. ERFs reduce the need for landfill disposal which is an important step up the hierarchy. But reducing waste in the first place and recycling as much as possible is even better.Back to Top Go to Next Step
Every week, recycling and rubbish is collected from homes and businesses. Everything that has been sorted for recycling is sent to specialist processing facilities. Food waste can be turned into energy at an anaerobic digestion plant. Anything placed in the non-recyclable waste bin is delivered to the Viridor ERF and transformed into energy.Back to Top Go to Next Step
Vehicles carrying the non-recyclable waste arrive at the ERF. First, they are weighed, they then continue to the tipping hall where they reverse up to the bunker to tip their loads.
The waste is mixed and managed in the bunker by large grab cranes. These cranes are operated by people in the Control Room, which has a large window overlooking the waste bunker. The waste is now ready to be used as a fuel to generate electricity and heat.Back to Top Go to Next Step
The grab cranes lift the non-recyclable waste into large feeder vessels, called hoppers. Hydraulic rams push the waste into the furnace. This is where the waste is burned at very high temperatures under controlled conditions. The ERF’s operations system works in compliance with the Industrial Emissions Directive, this ensures temperatures of the gases in the combustion chamber remain at a minimum of 850°C for at least two seconds – this ensures complete combustion takes place.
Air which is sucked in from the tipping hall, is injected into the furnace through holes under the furnace grates. This provides the oxygen needed for combustion (burning) to take place. It also creates a negative pressure in the tipping hall drawing air from the bunker into the process.Back to Top Go to Next Step
The fire in the furnace releases gases which are held at >850°C for more than 2 seconds before being fed into the boiler. Water flows through pipes around the boiler in the opposite direction to the hot gases. A heat exchange takes place, turning the water into steam. The steam is then superheated to around 400°C and 60 bar pressure. Finally, it is released to drive the turbine.Back to Top Go to Next Step
The superheated steam produced in the boiler is used to drive a turbine. The turbine is a key piece of equipment in the ERF as it converts the heat energy (steam) into mechanical (kinetic) energy. How does it do this? It’s actually very simple. The turbine has fan blades mounted on a rotor. The high-pressure steam turns the blades, and thus the rotor.
This rotary motion (kinetic energy) is used to run a generator which generates electricity. It’s a very similar process to the one used by traditional power stations. The big difference is that the fuel used is non-recyclable waste.Back to Top Go to Next Step
The power produced by the generator is exported to the electricity grid to supply homes, schools, shops, businesses and industry across the country. The Viridor ERF fleet produces enough electricity to power all the facilities and over 500,000 homes.
Steam produced during the process can be used in a heat network to provide heating and hot water to local homes and businesses via highly insulated pipes. When heat is used in this way it means that the ERF can be called a Combined Heat and Power (CHP) facility.Back to Top Go to Next Step
Once the heat has been recovered from the combustion gases in the boiler they are treated before they can be released into the atmosphere. Ammonia or urea, hydrated lime and activated carbon are added to remove nitrous oxides, acid gases and adsorb heavy metals, dioxins, furans and volatile organic compounds in the energy recovery process. The gases are treated and tested continuously. Screens in the control room report back live data and to ensure the right amount of cleaning is undertaken at all times.Back to Top Go to Next Step
Once the gases have been cleaned and filtered, they are released into the atmosphere through the flue stack (chimney). These hot gases condense to produce a plume of water vapour.
The ERF operates in compliance with the Environmental Permit that is issued by the environmental regulator, the Environment Agency (EA) in England, Natural Resources Wales (NRW) or the Scottish Environmental Protection Agency (SEPA). The permit sets strict limits on the emissions (gases) that are released into the atmosphere by the ERF. This means the ERF must comply with all the necessary regulations protecting both health and the environment.
Emissions from the ERF are continuously monitored and converted into 10 minute, half-hourly and daily averages.
For more information see our Emissions Management.Back to Top Go to Next Step
The air pollution control residue (APCr) captured by the bag filters (see step 10 - ‘Filter it’) is stored in a silo before being collected under controlled conditions by specialist vehicles.
APCr is taken to a licensed facility where it is recycled into aggregates for use in the construction industry.Back to Top Go to Next Step
The ash which is left after the waste has been burned (about 23% of the total) is called incinerator bottom ash (IBA). It contains anything which did not burn at around 850°C – this includes metals, concrete and glass. The IBA drops off the furnace grate onto a conveyor belt below. It is stored and then collected and taken to a licensed facility for recycling.Back to Top Go to Next Step
Once the metals have been separated out from the incinerator bottom ash, anything that’s left is crushed, screened for quality and treated to create an aggregate for road building and other construction products.Back to Top