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1 Thermal treatment is the release of energy from waste. This results in a change to the chemical structure of the waste and this change is not reversible 1.

2 The most common thermal treatment is incineration. Incineration is a thermal treatment in which waste is burned at high temperatures turning the carbon and hydrogen present in the original waste into carbon dioxide and water respectively. Less common are the advanced thermal treatments (ATT) such as gasification and pyrolysis in which the molecular structure of the original waste is transformed resulting in substances that are physically and chemically different from the original waste 2. They each have their advantages and disadvantages, with no one size fits all solution. The size and site of the plant will influence the type of technology that is appropriate. The use of waste heat in combined heat and power plants (CHP) significantly increases the overall efficiency of the process and the environmental benefits. Smaller sites may suit the ATTs which can operate at smaller scale. In 2010, the combustion of the biodegradable component of MSW provided 6.2% of the UK s total renewable electricity generation and 4.7% of total combined renewable heat and electricity generation 3. 1 Chartered Institution of Wastes Management (2013). of Wastes technical briefing note 2 Environmental Permitting Guidance; The Waste Incineration Directive; For the Environmental Permitting (England and Wales) Regulations 2010 Updated March 2010 Version 3.1 ( environment/policy/permits/ documents/ep2010 wasteincineration.pdf 3 DEFRA (2014) Energy from waste a guide to the debate. February 2014 (revised edition)available at uploads/system/uploads/attachment_ data/file/284612/pb14130-energywaste pdf accessed 11/03/14

3 Types of s Process Key Features Outputs Combustion/ Energy from Waste The combustion of typically unprepared (raw or residual) waste. To allow the combustion to take place a sufficient quantity of oxygen is required to fully oxidise the fuel. Temperatures are required of 850 C and above to prevent the formation of dioxins. The direct combustion of a waste usually releases more of the available energy compared to pyrolysis and gasification. It is a well-established technology with a proven track record. The waste is mostly converted into carbon dioxide and water and any non-combustible materials (e.g. metals, glass, stones) remain as a solid, known as Incinerator Bottom Ash (IBA). Metals can be removed from IBA by magnetic separation. Fly ash is also produced from the gas cleaning system. This normally contains lime and carbon and may be used to make plasterboard or sent to landfill. The heat produced can be used to generate electricity and the waste heat used for space or process heating. Pyrolysis The thermal degradation of a substance in the absence of oxygen. This process requires an external heat source to maintain the temperature required. Relatively low temperatures between 300 C and 850 C are needed. The gas can be utilised in combustion engines which can be configured in a combined heat and power configuration to maximise the efficiency of the system. The products of pyrolysing waste materials are a solid residue and a synthetic gas (syngas) or parts of this gas maybe condensed to produce a liquid fuel / chemical feedstock. The syngas is a mixture of gases (combustible constituents include carbon monoxide, hydrogen, methane and a broad range of other volatile organic compounds (VOCs). The syngas typically has a net calorific value (NCV) of between 10 and 20 MJ/Nm 3.*

4 Types of s continued Process Key Features Outputs Gasification Gasification could be seen as between combustion and pyrolysis in that it involves a partial oxidation of a substance. It is the thermal degradation of waste in an oxygen deficient environment so that there is not sufficient oxygen to allow the waste to be fully oxidised or full combustion to occur. The process is largely exothermic but some heat may be required to initialise and sustain the gasification process. Temperatures of above 650 C are required. The main product is a syngas, which contains carbon monoxide, hydrogen and methane. Typically, the gas generated from gasification will have a net calorific value (NCV) of 4-10 MJ/Nm 3.* A solid residue of non-combustible materials (ash) which contains a relatively low level of carbon is also produced. Plasma Gasification There are a number of applications for plasma technology; however for the treatment of waste it is likely to form part of a gasification or pyrolysis treatment option. Plasma treatment takes place in a second chamber subjecting the input materials to a high temperature process in order to break down tars and produce a cleaner syngas. A proposed plant in Nottinghamshire by Waste2Tricity will demonstrate the use of fuel cell technology alongside plasma gasification. This will produce up to 40% electricity from the same feedstock compared to combustion engines. The main products are a syngas lower in trace contaminants than from a purely gasification based process, melted metals and a vitrified glass from any inorganic components. *Natural Gas has a NCV of around 38Mj/Nm3

5 Types of s continued Process Key Features Outputs Autoclave The waste is subjected to steam under pressure, followed by mechanical sorting and separation of the sterilised waste. Temperatures of 120 C 170 C The resulting outputs from this heat/steam processing are relatively clean hard recyclables (tins, glass and plastics with no labels and most of the food waste removed) a fibrous material from the breakdown of paper, card and green/kitchen waste constituents, and a reject fraction. Mechanical Heat Treatment (e.g. Thermal drying) The waste is dried using externally applied heat (not under pressure), followed by mechanical sorting and separation of the sanitised waste. Similar outputs to Autoclave. Cement Kilns Refuse derived fuel (RDF) is used to provide between 20% and 40% of the energy requirement of a cement kiln as a replacement for fossil fuels. However it requires an RDF fuel that meets the appropriate cement kiln specifications. Substitute fuel

6 Glossary of Terms Term or Abbreviation Definition CHP Combined Heat and Power. The combined production of electricity and usable heat. Steam or hot water, which would otherwise be rejected when electricity alone is produced, is used for space or process heating. CV Calorific Value. This refers to the amount of heat released when a substance is burnt. Wastes with a high calorific value are suitable for deriving energy. MSW Municipal Solid Waste. This includes all waste under the control of local authorities or agents acting on their behalf. It includes all household waste, street litter, waste delivered to council recycling points, municipal parks and gardens wastes, council office waste, household waste recycling centres (HWRCs), and some commercial waste from shops and smaller trading estates where local authorities have waste collection agreements in place. It can also include industrial waste collected by a Waste Collection Authority with authorisation of the waste disposal authority. RDF/SRF Refuse Derived Fuel (RDF). The combustible fraction of municipal waste can be mechanically and/or thermally separated into RDF (sometimes referred to as Solid Recovered Fuel (SRF). This may be pelletised or utilised as a loose flock product in a controlled combustion process (either a dedicated incineration/gasification process or co-combusted in an industrial type application, for example a cement kiln or power station). RDF is produced in Mechanical Biological Treatment Anaerobic Digestion (MBT-AD) facilities. In Greater Manchester it is burned at Runcorn Energy Recovery Facility (ERF) to produce electricity.