Incineration

Co-incineration Plant

The Waste Incineration Directive (WID) defines an incineration plant as any stationary or mobile technical unit and equipment dedicated to the thermal treatment of waste with or without the recovery of the combustion heat generated. This includes the incineration of waste as well as other thermal treatment processes such as pyrolysis, gasification or plasma processes where substances resulting from the treatment are then incinerated. 8

The directive defines a co-incineration plant as any stationary or mobile plant whose main purpose is the generation of energy or production of material products, and:

• which uses waste as a regular or additional fuel, or
• in which waste is thermally treated for the purpose of disposal.

The WID definitions of incineration plant and co-incineration plant also include related operations and equipment around the plant.8

The Waste Incineration Directive (WID) is a European law which aims to prevent, or limit as far as practicable, negative effects on the environment from the incineration and co-incineration of waste. The Directive applies to most activities that involve the burning of waste, whether for disposal or when used as fuel.8

The Waste Incineration Directive was implemented in the UK in 2002 and 2003, by separate regulations for England and Wales, Scotland and Northern Ireland, in conjunction with the pollution prevention and control (PPC) regime. These regulations introduced strict regulatory controls and minimum technical standards for waste incinerators and co-incinerators. Note that other legal controls may also apply if you burn waste 8

The Landfill Directive requires the diversion of biodegradable municipal solid waste (BMW) from landfill to help protect the environment and reduce the amount of greenhouse gas emitted from landfill sites. The Incineration of waste is a successful way in helping to meet these requirements of the Landfill Directive. Incineration can also help reduce the reliance on other energy sources such as fossil fuels or nuclear. For Example in Sheffield an Energy from Waste facility has been built to deal with their residual municipal solid waste. The facility meets its own energy requirements and it also produces up to 21MW of electricity to export to the national grid and up to 60MW of heat which is used to supply heat and hot water to a significant part of the city centre (ice 2006).5

During the combustion process the volume and weight of the waste is reduced and transformed into various hot gases. Prior to any of these gases being emitted to atmosphere they are treated through numerous forms of emission reduction technologies, which result in an ash which can then go for further treatment or disposal. Energy is also produced from this process, which can be used for district heating and electricity generation. Where both electricity and heat are utilised from an incineration plant it may be termed a Combined Heat and Power (CHP) plant.

Incineration facts and figures in the UK

In England currently 10 percent of municipal waste is incinerated. By comparison, the European average is 17.3 percent, and Denmark incinerates 56 percent of its municipal waste.

Energy obtained from incineration can be used for local heating and power, but it may not always be practical to have such a scheme. 3

Typically 500kWh of electricity can be generated from one tonne of waste (20 to 22 percent efficient), although if a CHP system is also incorporated and the thermal energy is utilised then combined efficiencies of up to 85 percent are possible.1,6

Process of Incineration

Moving Grate Combustion

The waste to be treated is deposited from the waste collection vehicle into a storage bunker and it is fed from there by crane into a feed hopper. This waste then passes on to feeder rams to control the amount of waste entering into the combustion chamber. The waste moves through the combustion chamber by a series of inclined moving grate bars (known as a moving grate system) and the waste is burned. The energy that is produced by this process can then be used to produce electricity or heat.

The hot flue gases generated by the combustion process travel through the boiler, which transfers heat to water to produce steam to drive the turbines to create electricity. The ferrous metal is extracted from the incineration bottom ash (IBA). The IBA can be used as a secondary aggregate in construction projects or disposed of to landfill as inert waste. The flue gas passes through an emission treatment process regulated to the highest environmental standards to comply with the Waste Incineration Directive to reduce too a minimum any pollutants before it is released through the stack into the atmosphere.

Fluidised Bed Combustion

Before the waste is incinerated the non-combustible materials, for example large pieces of metal, are removed. Following this the waste is shredded to a particle size of less than 150mm. Fluidised bed combustion is thermally more efficient than moving grate incineration, but it produces a greater proportion of fly ash. There is also an energy cost in pre-treating the waste prior to combustion. It consists of a bed of particles, usually sand, through which a constant flow of air is pumped, which mixes the waste on the bed. The waste is fed into the combustion chamber where because of the mixing it is easier to burn at a lower temperature. This process produces lower nitrogen oxides (NOx) emissions than the moving grate system with the air emissions subject to the same controls and standards.

Environment

The pollutants which have the potential to damage the environment and human health are the production of the dioxins, acid gases, nitrogen oxides, heavy metals and particulates. These are produced in the incineration process and are largely present in the flue gases. The combustion of one tonne of MSW will generate 5200-6000Nm3 h-1 flue gases. The cleaning of the flue gases is an essential part of a modern incineration facility to reduce any emissions into the atmosphere to a level that meets the safety standards established in the Waste Incineration Directive. It involves a number of chemical and physical processes (CIWM 2003): 1

Legislation

The regulation of an incinerator is carried out by the relevant agency:

• England and Wales - Environment agency
• Scotland- SEPA
• Northern Ireland- Department of the Environment and Heritage Service

Environmental permits

Environmental permitting currently applies to England and Wales only. It combines pollution prevention and control (PPC) permits and waste management licensing (WML) into a single, modern, simpler system.

If you operate your business in Northern Ireland or Scotland, see the NetRegs guidance on pollution prevention and control and waste management licensing. 7

Pollution prevention and control permits

Businesses in Northern Ireland or Scotland, may need a pollution prevention and control (PPC) permit from an environmental regulator before it can operate. The PPC regulations contain lists of all the types of operations that require a permit. For example, will need a permit if your business has a production capacity above a certain level or you use certain hazardous substances.

There are separate PPC regulations in Northern Ireland and Scotland.

For businesses in England or Wales, see the NetRegs guidance on environmental permitting.6

The level of emissions that are allowed to be released from an incinerator must also comply with the EC Waste Incineration Directive (WID) (2000/76/EC).

For guidance see:

Ash disposal has to comply with various regulations and directives, including the Landfill Directive (2000/76/EC). The Landfill Directive aims to prevent or reduce the negative effects on the environment from the landfilling of waste 9.

For more information see: http://www.defra.gov.uk/environment/waste/topics/landfill-dir/

Ash disposal must also comply with the hazardous waste regulations.

References

• CIWM (2003), The Chartered Institution of Wastes Management, Energy from Waste: A Good Practice Guide
• Defra (2006), Key Facts about: Waste and Recycling http://www.defra.gov.uk/environment/statistics/waste/kf/wrkf06.htm
• Environment Agency, Environmental Facts and Figures: