Key environmental issues

Waste itself, and its management, are themselves a significant environmental issue. The thermal treatment of waste may therefore be seen as a response to the environmental threats posed by poorly or unmanaged waste streams.

The target of thermal treatment (see also Section 1.1) is to provide for an overall reduction in the environmental impact that might otherwise arise from the waste. However, in the course of the operation of incineration installations, emissions and consumptions arise, whose existence or magnitude are influenced by the installation design and operation. This section therefore, briefly, summarises the main environmental issues that arise directly from incineration installations (i.e. it does not include the wider impacts or benefits of incineration). Essentially these direct impacts fall into the following main categories:

 overall process emissions to air and water (including odour)

 overall process residue production

 process noise and vibration

 energy consumption and production

 raw material (reagent) consumption

 fugitive emissions – mainly from waste storage

 reduction of the storage/handling/processing risks of hazardous wastes.

Other impacts beyond the scope of this BREF document (but which can significantly impact upon the overall environmental impact of an entire project) arise from the following operations:

 transport of incoming waste and outgoing residues

 extensive waste pretreatment (e.g. preparation of waste derived fuels and the associated refuse treatment).

1.6.1 Process emissions to air and water

Emissions to air have long been the focus of attention for waste incineration plants. Significant advances in technologies for the cleaning of flue-gases in particular have lead to major reductions in the emissions to air.

However, the control of emissions to air remains an important issue for the sector. As the entire incineration process is usually under slightly negative pressure (because of the common inclusion of an induced draught extraction fan), routine emissions to air generally take place exclusively from the stack. [2, infomil, 2002]

A summary of the main emissions to air from stack releases (these are described in more detail in Section 3.2.1) is shown below:

 particulate matter, –particulate matter - various particle sizes

 acid and other gases, –including HCl, HF, HBr, HI, SO2, NOX, NH3 amongst others

 heavy metals, –including Hg, Cd, Tl, As, Ni, Pb, amongst others

 carbon comp. (non-GHG), –including, CO, hydrocarbons (VOCs), PCDD/F, PCB amongst others.

Other releases to air may include, if there is no measure to reduce them:

 odour, –from handling and storage of untreated waste

 green house gases (GHGs) –from decomposition of stored wastes e.g. methane, CO2

 dusts, –from dry reagent handling and waste storage areas.

The principle potential sources of releases to water (process dependent) are:

 effluents from air pollution control devices, e.g. salts, heavy metals (HMs)

 final effluent discharges from waste water treatment plants, e.g. salts, heavy metals

 boiler water - blowdown bleeds, e.g. salts

 cooling water - from wet cooling systems, e.g. salts, biocides

 road and other surface drainage, e.g. diluted waste leachates

 incoming waste storage, handling and transfer areas, e.g. diluted incoming wastes

 raw material storage areas, e.g. treatment chemicals

 residue handling, treatment and storage areas, e.g. salts, HMs, organics.

The waste water produced at the installation can contain a wide range of potentially polluting substances depending upon its actual source. The actual release made will be highly dependent on the treatment and control systems applied.

1.6.2 Installation residues production

The nature and quantity of residues produced are a key issue for the sector. This is because they provide both: (1) a measure of the completeness of the incineration process, and (2) generally represent the largest potential waste arising at the installation.

[64, TWGComments, 2003], [1, UBA, 2001] Although the types and quantities of residue arising varies greatly according to the installation design, its operation and waste input, the following main waste streams are commonly produced during the incineration process:

 ashes and/or slag

 boiler ashes

 filter dust

 other residues from the flue-gas cleaning (e.g. calcium or sodium chlorides)

 sludge from waste water treatment.

In some cases, the above waste streams are segregated; in other cases, they are combined within or outside the process.

Some thermal treatment residues (most commonly vitrified slags from very high temperature processes) can be used directly without treatment. Substances which can be obtained after the treatment of the bottom ashes are:

 construction materials

 ferrous metals

 non ferrous metals.

In addition, some plants using wet FGC processes with additional specific equipment recover:

 calcium sulphate (Gypsum)

 hydrochloric acid

 sodium carbonate

 sodium chloride.

Of these outputs, although very dependent upon the waste type, bottom ashes are generally produced in the largest quantities. In many locations, often depending on local legislation and practice, bottom ash is treated for re-cycling as an aggregate replacement.

Figure 1.2: Bottom ash recycled and deposited from MSWI in 1999

*means incomplete data [42, ISWA, 2002]

Residues produced from the flue-gas cleaning are an important source of waste production. The amount and nature of these varies, mainly according to the types of waste being incinerated and the technology that is employed.

1.6.3 Process noise and vibration

[2, infomil, 2002] The noise aspects of waste incineration are comparable with other heavy industries and with power generation plants. It is common practice for new municipal waste incineration plants to be installed in completely closed building(s), as far as possible. This normally includes operations such as the unloading of waste, mechanical pretreatment, flue-gas treatment, and the treatment of residues. Usually, only some parts of flue-gas cleaning systems (pipes, tubes, SCR, heat exchangers, etc.), cooling facilities and the long-term storage of bottom ash are carried out directly in the open air.

The most important sources of external noise are:

 vehicles used for the transport of waste, chemicals and residues

 mechanical pretreatment of waste, e.g. shredding, baling, etc.

 exhaust fans, extracting flue-gases from the incineration process and causing noise at the outlet of the stack

 noise, related to the cooling system (from evaporative cooling, especially air cooling)

 turbine generation noise (high level so usually placed in specific sound-proofed buildings)

 boiler pressure emergency blowdowns (these require direct release to atmosphere for boiler safety reasons)

 compressors for compressed air

 noise related to the transport and treatment of bottom ash (if on the same site).

SCR systems and flue-gas ducts give rise to little noise and are often not inside buildings. Other installation parts are not usually significant for external noise production but may contribute to a general external noise production by the plant buildings.

1.6.4 Energy production and consumption

Waste incinerators both produce and consume energy. In a large majority of cases, the energetic value of the waste exceeds the process requirements. This may result in the net export of energy.

This is often the case with municipal waste incinerators in particular.

Given the total quantities of waste arising, and its growth over many years, the incineration of waste can be seen to offer a large potential source of energy. In some MSs this energy source is already well exploited. This is particularly the case where the use of CHP is used. Energy issues are discussed in more detail later in this document (see Sections 3.5 and 4.3).

[64, TWGComments, 2003]

Figure 1.3 below shows the production of heat and electricity from municipal waste incineration plants for various countries in 1999:

Figure 1.3: Energy production by municipal waste incinerators in Europe (1999)

* means incomplete data [42, ISWA, 2002]

Most wastes contain biomass (to differing degrees). In such cases, the energy derived from the biomass fraction may be considered to substitute for fossil fuel and therefore the recovery of energy from that fraction be considered to contribute to a reduction in the overall carbon dioxide emissions from energy production. In some countries, this attracts subsidies and tax reductions.

[64, TWGComments, 2003]

Energy inputs to the incineration process can include:

 waste

 support fuels, (e.g. diesel, natural gas):

 for start-up and shutdown

 to maintain required temperatures with lower CV wastes

 for flue-gas reheating before treatment or release

 imported electricity:

 for start-up and shutdown phases when all lines are stopped and for plants without electricity generation.

(Note: some of the above energy inputs contribute to steam/heat production where boilers are

Energy production, self-consumption and export can include:

 electricity

 heat (as steam or hot water)

 syngas (for pyrolysis and gasification plants that do not burn the syngas on site).

The efficient recovery of the energy content of the waste is generally considered to be a key issue for the industry.

[74, TWGComments, 2004]

1.6.5 Consumption of raw materials and energy by the installation

Waste incineration plants (process dependent) may consume the following:

 electricity, for process plant operation

 heat, for specific process needs

 fuels, support fuels (e.g. gas, light oils, coal, char)

 water, for flue-gas treatment, cooling and boiler operation

 flue-gas treatment reagents, e.g. caustic soda, lime, sodium bicarbonate, sodium sulphite hydrogen peroxide, activated carbon, ammonia, and urea

 water treatment reagents, e.g. acids, alkalis, tri-mercapto tri-azine, sodium sulphite, etc.

 high pressure air, for compressors.

[74, TWGComments, 2004]

Im Dokument Integrierte Vermeidung und Verminderung der Umweltverschmutzung (IVU) BVT-Merkblatt über beste verfügbare Techniken der Abfallverbrennung Juli 2005 mit ausgewählten Kapiteln in deutscher Übersetzung (Seite 55-59)