The UK is obliged under the EU’s revised Waste Framework Directive to apply the waste hierarchy. This ranks waste management options in order of environmental preference
The first priority is waste reduction. Recovering energy from waste is only appropriate for waste that cannot be prevented, reused or recycled with less greenhouse gas emissions.
Energy recovery can be a sustainable option for waste that would otherwise go to landfill, so avoiding landfill methane emissions.
Our aim is to get the most energy out of genuinely residual waste, not to get the most waste into energy recovery.
Different types of technologies
Energy from waste can be generated in a variety of ways:
Conventional technologies
- Direct combustion (incineration) of dry biomass waste such as wood waste, straw and poultry litter, or the biomass part of municipal waste and some commercial and industrial, and construction and demolition wastes. The heat generated can be used directly to warm homes and buildings, or to generate electricity using a steam turbine. Where waste is combusted in a combined heat and power unit it is possible to produce both heat and power at greater efficiencies.
- Combustion of waste-derived fuel, such as the methane produced from landfill (landfill gas).
The methane can be used in the same way as for combustion plants or it can be injected into the national gas grid.
- Anaerobic digestion of wet biomass waste such as sewage sludge, animal manure and slurry, and waste food. This is a natural process in which micro-organisms break down the organic matter, in the absence of oxygen, to produce biogas (mainly a mixture of around 60% methane and 40% carbon dioxide) and digestate (a nitrogen rich fertiliser). The biogas can be burned directly in a gas boiler to produce heat or burnt in a combined heat and power (CHP) unit to produce heat and electricity. Alternatively, the biogas can be cleaned to remove the carbon dioxide and other substances, to produce biomethane. This can be injected into the national gas grid to be used in the same way as natural gas, or used as a vehicle fuel.
Advanced conversion technologies
A number of innovative advanced, high temperature processes are beginning to emerge. These have the potential to be more efficient than conventional processes and can offer a range of different types of energy from bio-based wastes, including wood waste and municipal wastes:
- Gasification produces a combustible gas which is a mixture of carbon monoxide, hydrogen, carbon dioxide and methane. This gas can be used directly to generate heat and electricity. Alternatively, it can be upgraded to an ultra clean gas called syngas.. This can be used to manufacture either biomethane, which can be injected into the national gas grid, or transport fuels such as hydrogen, ethanol, synthetic diesel or jet fuel
- Pyrolysis can be used to produce either a combustible gas, oil or solid char (sometimes known as biocoal). In the future, it will be possible to upgrade pyrolysis oil to produce petrol and diesel using oil refining techniques.
The choice of technology for any project depends on the type of waste available, local circumstances and finance.
Environmental controls
All energy from waste plants must comply with regulations concerning environmental protection, animal by-products, duty of care, health and safety, waste handling and planning permission.
Barriers
There are a number of challenges facing energy from waste projects, even for the established technologies, and these need to be overcome for the sector to expand.
The outcome of the Government’s Review of Waste policies (links to Defra website) in England was published on 14 June 2011. This looks at all aspects of waste policy and delivery in England to ensure we are taking the necessary steps towards creating a ‘zero waste’ economy, where resources are fully valued, and nothing of value gets thrown away.
The review recognises the important part that energy from waste can play in helping to meet renewable energy targets, diversifying supply, and providing economic opportunities. It suggests that renewable electricity generated from waste through combustion technologies could almost treble from the current 1.2TWh to between 3.1TWh and 3.6TWh by 2020.
It outlines a number of actions for Government, aimed at overcoming barriers to deployment to ensure we get the most energy out of genuinely residual waste. Actions include:
- improving communications and information on energy from waste technologies
- exploring ways to help communities benefit from hosting energy from waste infrastructure
- supporting industry in developing supply chains for waste feedstocks; and
- ensuring that waste management legislation does not have unintended consequences on the development of energy plants.
Anaerobic Digestion Strategy and Action Plan
The Anaerobic Digestion Strategy and Action Plan (links to Defra website) was also published on 14 June. The Strategy sets out a vision for Anaerobic Ddigestion (AD), with an estimate of potential that could reach between 3-5 TWh for heat and electricity by 2020.
The accompanying Action Plan is the result of Defra, DECC and other Government departments working closely with industry to identify the key barriers to the development of AD and the actions that are needed to overcome them. These include:
- improving the dissemination of information, particularly on regulatory controls
- guidance on the costs and benefits of AD, including best practice projects
- tackling specific barriers, such as the cost and complexity of connection to the gas grid
- developing skills and training for AD operators
- building markets for digestate; and
- understanding the barriers to the use of biomethane as a transport fuel.
Government and Industry will continue to work together to implement the agreed actions.