- Incineration - Gasification - Pyrolysis

- Incineration - Gasification - Pyrolysis
THERMAL WASTE TREATMENT

Background Types of thermal treatments: Incineration, pyrolysis and gasification These thermal technologies are designed to recover energy (in the form of heat, electricity or fuel) and can contribute to the diversion of BMW from landfill. Incineration is the oxidation of the combustible material in the waste to produce heat, water vapour, nitrogen, carbon dioxide and oxygen. Depending on the waste composition, other emissions may be formed including, carbon monoxide, hydrogen chloride, hydrogen fluoride, nitrogen oxides, sulphur dioxide, volatile organic carbon, dioxins and furans, polychlorinated biphenyls, heavy metals, etc. The gasification and pyrolysis of solid materials is not a new concept. It has been used extensively to produce fuels such as charcoal and coke or producer gas. Charcoal and coke are produced by pyrolysing wood and coal respectively and producer gas is a combustible gas produced by the gasification of coke in the presence of air and steam

Background It is only in recent years that such pyrolysis and gasification have been commercially applied to the treatment of MSW. The development of pyrolysis and gasification technologies is in its infancy in the UK but large scale plants have been built and are in operation in Europe, North America and Japan (as shown in Table 1) In short, combustion directly releases the energy in the waste, whereas pyrolysis and gasification thermally treat the waste to generate secondary products (gas, liquid and/or solid) from which energy can be generated. TT are capital intensive facilities and have a design life of 15 – 25 years.

Table 1. TT facilities

Heating value Moisture content and ash represent the non-combustible component of the MSW. Moisture and ash are undesirable in MSW as they add weight to the fuel without adding to the heating value. Furthermore, ash retains heat when removed from the furnace; causing useful heat to be lost to the environment. The volatile matter and the fixed carbon content are the preferred indicators of the combustion capability of MSW. Volatile matter: the portion of MSW converted into gas as the temperature increases. Gasification occurs before the onset of combustion. Fixed carbon: the solid carbon residue that has settled on the furnace grates. Combustion occurs in the solid state, i.e., on the surface of this ‘char’ material. The rate of combustion is affected by the temperature and surface area of the char. A waste fuel with a high percentage of fixed carbon will require a longer retention time in the combustion chamber to achieve complete combustion as compared with a fuel low in fixed carbon. % fixed carbon = 100% - % moisture - % ash - % volatile matter

Proximate analysis data for the combustible components of MSW and bulk samples of MSW are presented in Table 2 above

Heating value Energy content of OFMSW determined by (i) combusting samples in a full-scale boiler and measuring steam output, (ii) using a laboratory bomb calorimeter, or (iii) calculation from elemental composition (i.e. ultimate analysis). Most data on the energy content of MSW are based on the bomb calorimeter tests. Heat of combustion: the energy stored within the chemical bonds of a material. This heat released when material is burned. Two significant heat of combustion parameters: high heating value and low heating value. high heating value (HHV): includes the heat of vaporization of water molecules generated during the combustion process. The reaction for the combustion of cellulose and the consequent formation of water is: HHV (MJ/kg) = (C) (H) – (O) (S)

Heating value How is heat value expressed?
Low heating value (LHV): subtracting the heat of vaporization of water. This value represents the net heat available during the incineration of MSW. Where W represents the % mass of water and H the wt % of H in the waste How is heat value expressed? Typical units – BTU per pound. Examples: Food wastes 2,000 BTU/lb Paper 7,200 BTU/lb Plastics 14,000 BTU/lb Wood 8,000 BTU/lb MSW 5,000 BTU/lb LHV (MJ/kg) = HHV (in MJ/kg) – (W + 9H)

Example 1 A carbonaceous waste given by the empirical formula C65.5H102.3O40.8N1.1 is to be incinerated. Proximate and elemental analysis of the waste are as follows: Calculate the gross heat value and net heat value of this waste as received Proximate analysis % Elemental analysis Moisture 4.8 Carbon 47.36 Noncombustibles 6.2 Hydrogen 6.25 Oxygen 39.25 Nitrogen 0.85 Sulfur 0.19 Ash 6.10

Difference between Pyrolysis, Gasification and Incineration
Incineration usually involves the combustion of unprepared (raw or residual) MSW. To allow the combustion to take place a sufficient quantity of oxygen is required to fully oxidise the fuel. Typically, incineration plant combustion (flame) temperatures are in excess of 850ºC and the waste is converted into carbon dioxide and water. Any noncombustible materials (e.g. metals, glass) remain as a solid, known as Bottom Ash, that contains a small amount of residual carbon

Pyrolysis is the thermal degradation of a substance in the absence of oxygen. This process requires an external heat source to maintain the temperature required. Typically, relatively low temperatures of between 300ºC to 850ºC are used during pyrolysis of materials such as MSW. The products produced from pyrolysing materials are a solid residue and a synthetic gas (syngas). The solid residue (sometimes described as a char) is a combination of non-combustible materials and carbon. The syngas is a mixture of gases (combustible constituents include carbon monoxide, hydrogen, methane and a broad range of other VOCs). A proportion of these can be condensed to produce oils, waxes and tars. The syngas typically has a net calorific value (NCV) of between 10 and 20 MJ/Nm3. If required, the condensable fraction can be collected by cooling the syngas, potentially for use as a liquid fuel.

Gasification can be seen as between pyrolysis and combustion in that it involves the partial oxidation of a substance. This means that oxygen is added but the amounts are not sufficient to allow the fuel to be completely oxidised and full combustion to occur. The temperatures employed are typically above 650°C. The process is largely exothermic but some heat may be required to initialise and sustain the gasification process. 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 MJ/Nm3. The other main product produced by gasification is a solid residue of noncombustible materials (ash) which contains a relatively low level of carbon. For reference, the calorific value of syngas from pyrolysis and gasification is far lower than natural gas, which has a NCV of around 38 MJ/Nm3.

Figure 1 Levels of air (oxygen) present during pyrolysis, gasification and combustion processes for MSW.

Thermal treatment in Malaysia
In Malaysia, hazardous waste such as clinical waste and toxic industrial waste is subjected to incineration Process There are small-scale capacity of MSW incinerators operating on islands (e.g. Langkawi, Tioman, Labuan). Given the space constraint and nature of waste on the island, thermal treatment technology is the best waste management option for the islands Langkawi Incinerator: use a rotary kiln and an air injection system to ensure continuous combustion. Sited on the existing Kilim landfill, Kuah, with 100 MT/day of solid waste capacity MSW screened and size reduction prior to treatment, recyclables sorted out from the TTP waste feed and set aside for recycling. The TTP equipped with a water-tube boiler to produce steam, potentially 1 MW Air pollution control includes a cyclone, a neutralization reactor and a baghouse filter. Cyclone: filters heavier and larger particulates (larger than 25 μm), efficiency rate of 70%. Baghouse filter: capture smaller dust particles, termed as fly ash, which are collected, stored and disposed accordingly. Has an efficiency rate of 99.8%. Flue gas will go through a neutralization reactor upon exit from the cyclone and prior to entering the baghouse filter to neutralize acidic gases and to hinder dioxin formation.

Any legislation in Malaysia about incineration?
In Malaysia, there is no regulation or guidelines specifically for air pollution emission from waste incinerators Air pollution emission from various sources have to comply with Clean Air Act Regulations The Clean Air Regulation 8, 280/1978 requires that written permission be sought from the Department of Environment (DOE), Ministry of Science, Technology and Environment for the construction and operation of an incinerator Department of Environment (DOE) adopted certain standards in line with international standard such as: United States Environmental Protection Agency (USEPA) European Standards (Directive 2000/76/EC) on the incineration of waste

Limits of pollutants imposed by European Standards (Daily average values)

Limits of pollutants imposed by European Standards (Average values of a minimum 30 minutes and a maximum of 8 hours) Limits of pollutants imposed by European Standards (Average values over a sample period of a minimum 6 hours and a maximum 8 hours)

INCINERATION

Figure 2 The incineration process

Advantages of incineration over landfill
Disadvantages of incineration over landfill Can be carried out near the point of waste collection. In some cities, the number of landfill sites close to the point of waste generation are becoming scarcer, resulting in transport of waste over long distances The waste is reduced into a biologically sterile ash product which for municipal solid waste is approximately 10% of its pre-burnt volume and 33% of its per-burnt weight Incineration producers no methane, a GHG A low-cost source of energy to produce steam for electric power generation, industrial process heating or hot water for district heating The bottom ash residue can be used for materials recovery or as secondary aggregates in construction Incineration is the best practicable environmental option for many hazardous wastes such as highly flammable, volatile, toxic and infectious waste Much higher costs and longer pay-back periods, due to the high capital investment There is sometimes a lack of flexibility in the choice of waste disposal options once the incineration route is chosen; because of the high capital cost the incinerator must be tied to long- term waste disposal contracts Incinerator design based on a certain calorific value for the waste. Removal of materials such as paper and plastics for recycling may reduce the overall calorific value of the waste and consequently may affect incinerator performance Whilst modern incinerators comply with the existing emissions legislation there is some public concern that the emitted levels may still have an adverse effect on health The incineration process still produces a solid waste residue which requires management

3 T’s Factors influencing the completeness of combustion- temperature, time and turbulence
Temperature: Each combustible substance has a minimum ignition temperature that must be attained in the presence of oxygen for combustion to be sustained. Above the ignition temperature, heat is generated at a higher rate than it loses to the surroundings, which makes it possible to maintain the elevated temperature necessary for sustained combustion. Time: the residence time of the input wastes in the high-temperature region of the combustion zone should exceed the time required for combustion to take place. Such a requirement will affect the size and shape of the furnace. Turbulence: (e.g. the thorough mixing of MSW as it passes through the combustion chamber) will expose particle surfaces to oxygen and high temperatures and will speed the evaporation of liquids for combustion in the vapor phase. Inadequate mixing of combustible gases and air in the furnace will lead to the generation of PICs, even from a unit containing sufficient oxygen

Combustion concept An aerobic thermal destruction process resulting in the transformation of solid waste to ash, gases, and heat energy. To achieve efficient combustion with a minimum of air pollutant emissions the correct amount of air must be available to the combustion chamber. This ‘stoichiometric air’ is needed to bring the combustion reactions to completion and avoid generation of any products of incomplete combustion (PICs). The reaction for combustion of an organic material in MSW: The process is much more complex, however, since not all the hydrocarbons are converted into carbon dioxide and water; and other components of the waste such as sulfur and nitrogen are also oxidized, as follows:

Example 2 A carbonaceous waste given by the empirical formula C65.5H102.3O40.8N1.1 is to be incinerated. Proximate and elemental analysis of the waste are as follows: Calculate the volume of air needed for the complete combustion of 1000 kg (1 metric ton) of the input material. Proximate analysis % Elemental analysis Moisture 4.8 Carbon 47.36 Noncombustibles 6.2 Hydrogen 6.25 Oxygen 39.25 Nitrogen 0.85 Sulfur 0.19 Ash 6.10

Incineration technology overview
Incinerator with energy recovery typically comprise the following key elements: waste reception and handling combustion chamber energy recovery plant emissions clean-up for combustion gases bottom ash handling and air pollution control residue handling Waste Reception and Handling MSW from the waste collection vehicle are tipped into a bunker where it is mixed. Mixing helps blend the waste to ensure that the energy input (calorific value of the waste feed) to the combustion chamber is as even as possible. Raw MSW energy content : MJ/kg, RDF energy content: 17MJ/kg Increase in the energy content of RDF is achieved due to the drying of the waste (removal of water) and the removal of recyclables (glass, metals) and inerts (stones etc), which do not contribute to the energy content of the waste. Therefore, the remaining waste going into the RDF mainly comprises wastes with significant energy content, plastics, dried biodegradable materials, textiles etc.

Combustion Technology There are four combustion technologies that can be employed to burn MSW or RDF. A brief overview of the main combustion technologies is presented in Table 3 (opposite).

Moving grate Combustion chamber Sec. Air Prim. Air Waste Funnel Slag Water basin Roll type grate Stair type grate

Rotary kiln Rotary kiln installation Inside Rotary kiln

Fluidised bed incinerator

Energy Recovery Recovery of energy from incineration of MSW is achieved through utilization of the combustion heat through a boiler to generate steam, where up to 80% total available energy in the waste can be retrieved this way The steam can be used for the generation of power via a steam turbine and/or used for heating. An energy recovery plant producing both heat and power referred to as a Combined Heat and Power (CHP) Plant is the most efficient option overall for utilising recovered energy from waste via a steam boiler. An incinerator producing exclusively heat can have a thermal generating efficiency of around %; this heat may be used to raise steam for electrical generation at approximately % efficiency. Emissions Control for Releases to Atmosphere To meet the emissions limits, the combustion process must be correctly controlled and the flue gases cleaned prior to their final release. A common approach for control of emissions is as follows:

ammonia injection into the hot flue gases for control of NOx emissions lime or Sodium Bicarbonate injection for control of SO2 and HCl carbon injection for capture of heavy metals filter system for removal of fly ash and other solids (lime or bicarbonate and carbon) The control of CO, VOCs and dioxins in terms of their concentration is primarily though correct combustion conditions being maintained. The clean-up of the flue gases will produce solid residues comprising fly-ash, lime/bicarbonate and carbon. These residues are usually combined (although some systems may separate fly ash and other components) and are classified as hazardous waste, therefore their disposal must be undertaken in accordance with relevant regulations and guidance. Typically, their production will be around 2% - 6% of the weight of the waste entering the incinerator.

Dioxin Filter Scrubber Quencher
Flue Gas Cleaning Method Flue Gas Emission in accordance to EU Standard prior to discharge to atmosphere Continuous Emission Monitoring System Step 3 : Dioxin Treatment Dioxin Filter Step 2: Flue Gas Cleaning to remove dust and acidic gases Scrubber Step 1: Flue Gas Cooling Quencher

Bottom Ash Handling The main residual material from the incineration of MSW is referred to as “bottom ash”. This is the residual material in the combustion chamber and consists of the noncombustible constituents of the waste feed. The bottom ash typically represents around 20% - 30% of the original waste feed by weight, only about 10% by volume. The bottom ash is continually discharged from the combustion chamber and is then cooled. The amount of ash will depend on the level of waste pre-treatment prior to entering the incinerator and will also contain metals that can be recovered for recycling.

Summary: The three main issues of incineration
The three main issues: (i) air emissions (ii) residual incinerator ash (iii) dioxin Air emissions The combustion of any substance will generate byproduct emissions that could be released to the air air emissions are usually associated with metals, mercury, lead, cadmium, organics such as dioxins and furans, acid gases, particulate matter such as dust and grit People can be exposed to emissions directly by inhaling contaminated air, ingesting, having skin contact with contaminated soil and dust. can also occur indirectly by eating foods that have been contaminated with these substances Residual incinerator ash generates ash representing about 10% by volume and 25-35% by weight of the waste incinerated. Ash can divided into two categories:

Summary: The three main issues of incineration
bottom ashcompletely or partially combusted material that passes through or is discharged from the combustion grate. fly ashparticulate matter captured from flue gas by the air pollution control system; it could include scrubber residue, bag house dust, and what is shaken from precipitators. Dioxin Dioxins are the most notorious pollutants associated with incinerators Cause a wide range of health problems including cancer, immune system damage, reproductive and developmental problems. Dioxins bioaccumulation, selectively building up in the fatty tissues of living organisms, and they biomagnified, meaning that they are passed up the food chain from prey to predator Particular concern because they are ever-present in the environment

Markets and outlets for the outputs
4 Markets and outlets for the outputs Incineration processes all produce a solid residue (bottom ash). Some systems are also designed with mechanical preparation and sorting equipment to extract recyclables before or after combustion. The table summarises the key outputs from incineration processes.

Materials Recycling The IBA produced can be potentially recycled as a secondary aggregate, used as fill or in masonry products’ However, the recycling of IBA would need to be undertaken in accordance with relevant legislation and guidance. metals (ferrous and sometimes non-ferrous) almost always are recovered from Incineration processes. However, the extraction of materials for recycling prior to combustion contributes more to recycling targets Energy Recovery Incineration processes are designed to recover energy from the waste processed by generating electricity and / or heat for use on site and export off site. The useful energy that can be generated from an incineration plant using a boiler to generate steam is presented in Table 5.

5

PYROLYSIS AND GASIFICATOIN

Advantages of Pyrolysis and Gasification over Incineration
Disadvantages of Pyrolysis and Gasification over Incineration Less oxygen, thus fewer air emissions Plants are modular; made up of small units which can be added to or taken away as waste streams or volumes change and are therefore more flexible and can operate at a smaller scale than mass-burn incinerators. They are quicker to build. Produce more useful products – gases, oils and solid char useful as a fuel, or purified and used as a feedstock for petro-chemicals and other applications. The syngas may be used to generate energy more efficiently, if a gas engine (and potentially a fuel cell) is used Unless they only deal with truly residual waste, the processes will undermine recycling and composting. Any fuel produced will not make up for the energy spent in manufacturing new products Disposal of ash and other by-products may be required, though some companies claim that their process makes this easier than for incineration ash. whilst incineration can only generate energy less efficiently via steam turbines.

Thermal treatment (TT) technology overview
The actual plant design and configuration of TT facilities will differ considerably between technology providers. However, an ATT plant will typically consist of the following key elements: Waste reception, handling and pretreatment; Thermal treatment reactor; Gas and residue treatment plant (optional); Energy recovery plant (optional); and Emissions clean-up. Figure 3 describes the generic process flows for TT technologies.

Figure 3 describes the generic process flows for TT technologies.

The two most important variables in a pyrolysis system are the heating rates (how rapidly the fuel is brought to a high temperature) and the final temperature. The ranges of these are listed in Table below: The choices of these variables, heating rate and temperature, determine the products obtained from the pyrolysis system. At very high temperatures and slow heating, the product is mostly gas, while at very slow heating rates and low temperature, mostly solid product results Heating rate °C/sec Temperature °C Slow <1 Low 500 to 750 Intermediate 5 to 100 750 to 1000 Rapid 500 to 106 High 1000 to 1200 Flash > 106 Very high > 1200

How it works Waste reception, handling and pre-treatment
The pyrolysis and gasification process treats the biodegradable materials present in MSW (e.g. paper,card, putrescible waste, green waste, wood), as well as plastics. Non combustible materials and recyclables (typically metals and glass) are removed prior to the primary treatment reactor stage. The feed material might require processing to remove excess moisture and shredding to reduce the size. TT processes may be used in conjunction with other waste treatment technologies such as Mechanical Biological Treatment (MBT) and Mechanical Heat Treatment (MHT). Many MBT/MHT plant are designed to produce a fuel stream (primarily composed of paper, card and plastics) as one of the outputs from the process. This is commonly referred to as Refuse Derived Fuel or RDF. This may be more amenable to processing in a TT plant rather than raw MSW.

How it works Thermal Treatment Reactor
The thermal treatment process, whether pyrolysis or gasification, will produce syngas and solid residue. The composition of the syngas and solid residue will depend on the process conditions employed, which include operating temperature, oxygen level, heating rate and residence time in the reactor. The main types of thermal treatment units available, their application and operating conditions are summarised in Table 2. There are also other factors influencing the process such as direction of gas flow (e.g. horizontally or vertically).

Table 2. Treatment reactors

How it works Gas and Residue Treatment Stages
Solids will be discharged from the process which include metals together with carbon. The level of carbon is small for gasification; but significant in pyrolysis Larger particles of solids in the thermal treatment reactor are usually discharged as bottom ash and slag. Lighter ash is usually collected when the gas is separated with the use of cyclones and ultimately filters. In addition, volatile metals such as lead, tin, cadmium and mercury will be carried in the gas until such point that the gas is cooled for them to be sufficiently condensed. Energy Recovery/Utilisation of Syngas One of the potential benefits of pyrolysis and gasification is that the syngas can be used in a number of different ways. In terms of producing energy, the most common configuration is to burn the syngas in a boiler to generate steam. The steam can then be used to generate electricity by passing it through a steam turbine and, if there is a demand local to the plant, for heating. Using the heat in addition to generating electricity improves the overall energy efficiency of the system significantly.

How it works The syngas can also be used to fuel a dedicated gas engine. A syngas from a very well run gasifier, or further processed for example by reforming, may be suitable for use in a gas turbine. Running these types of plant on syngas is still in its infancy and would require cleaning and cooling prior to use. To minimise costs for energy generation the TT plant could be located adjacent to an existing power plant and the syngas transferred to it. Syngas could also be used as a chemical feedstock, but would require the treatment plant to be local to the end user, in order to be a practical solution. This would require very high gas cleanliness; pollutants, notably sulphur and halogens, may need to be removed prior to combustion of the gas. Alkalis such as lime and sodium hydroxide are the favoured reagents for removal of the halogen streams. Sulphur can be removed by a variety of routes, largely dependant on the initial concentration Syngas from waste has potential as hydrogen source, which could have applications in both power generation and as a vehicle fuel. There would however be significant purification and reforming required before the gas would be of an appropriate quality for power generation (in turbines) or transport (in fuel cells).

How it works The advantages of using TT plants to produce the syngas would arise from their relatively small scale, flexibility to different inputs and modular development. Producing syngas to serve multiple end uses could complicate delivery of the plants but it could provide a higher degree of financial security.

Examples of TT technologies
Waste Gen (Tech Trade) Hamm Germany A pyrolysis plant that processes a pre-prepared RDF to produce a syngas that is immediately burnt in a dedicated burner in an otherwise coal fired power station boiler. The resulting char after recovery of metals using magnets and aggregate, using a ballistic separator, is fed into the station coalbunkers. Fuel is delivered to the plant in bales or bulk form, from a range of RDF producers. The fuel is conveyed to the two rotary kiln, pyrolyser, units (20m in length x 2.8m in diameter). Natural gas burners heat the pyrolysis drums. The two pyrolysis drums replace 10% of the fuel input to a coal fired 330Mwe generating set.

Examples of TT technologies
KBI Waste & Energy Solutions GmbH A Mechanical & Biological Treatment (MBT) plant followed by an oxygen blown ‘down draught’ gasifier. The waste pre-treatment and the gasifier helps to produce quality and consistent gas production and meet emission limits. Received waste is dried in a rotating compost drum and recyclates are removed. The waste then passes to a feed preparation area where additives such as coke, (typically 17%) and limestone are introduced prior to gasification. In the gasifier oxygen is added at several points down the gasifier progressively raising the temperature towards the maximum, normally 1500°C. Additional feeds of steam and natural gas are used so as to control the composition of the produced gas. The gas is to be used for power generation via a gas turbine set. The gas is burned in a conventional gas turbine set and the exhaust gas from the turbine is used to raise steam. Some of the steam / electricity is used by the process with the excess available for export.

TT processes will all produce a gas (usually for energy recovery) and a solid residue (slag, ash or char). Some facilities are also designed with mechanical preparation and sorting equipment to extract recyclables. Table 3 summarises the key outputs from ATT processes. Materials Recycling Recyclables derived from either the front end preparation stage of a TT plant or metals extracted from the back end of the process (i.e. out of the ash) are typically of a lower quality than those derived from a separate household recyclate collection system, and generally have a lower value accordingly. The types of materials recovered from TT processes almost always include metals (ferrous and non-ferrous), usually from the front end of the process. Metal removal can help enhance overall recycling levels and enable recovery of certain constituent parts that would not otherwise be collected in household systems (e.g. steel coat hangers, scrap metal etc.).

Table 3: Examples of outputs from gasification and pyrolysis processes

Pyrolysis plants produce a bottom residue that contains significant amounts of carbon. This will need to be disposed of to landfill, or treated further to reduce the carbon content for example by gasification or combustion. If treated further the final bottom residue could then be recycled as a secondary aggregate. Gasification tends to produce a bottom residue which has a lower carbon content and has usually been melted or fused, and this could therefore be recycled as aggregate. The recycling of bottom ash would need to be undertaken in accordance with relevant legislation but is likely to be of equivalent or potentially better quality than incinerator bottom ash, which is currently recycled in aggregate applications. Energy TT processes are designed to recover energy from the waste processed either in the form of fuel production (liquid or gas) or combusting the syngas to generate electricity and/or heat for use on site and export off site. There is also potential for the syngas to be utilised in vehicles, after reforming to produce hydrogen. It is envisaged that the initial market for the hydrogen would be public transport fleets using fuel cell vehicles.

PLANNING ISSUES

Key Issues The key issues that will need to be considered when planning a TT facility are: Plant/Facility Siting; Traffic; Air Emissions / Health Effects; Dust / Odour; Flies, Vermin and Birds; Noise; Litter; Water Resources; Visual Intrusion; and Public Concern

Planningissues Plant Siting
TT processes can be similar in appearance and characteristics to various process industries. It would often be suitable to locate facilities on land previously used for general industrial activities Facilities are likely to require good transport infrastructure. Such sites should either be located close to the primary road network or alternatively have the potential to be accessed by rail or barge The location of such plants together with facilities producing RDF (such as MBT and MHT facilities) could be advantageous. The potential for export of energy to host users or the national grid should also be a key consideration in the siting of TT facilities. Consideration should always be given to utilising not only the electricity from the plant but also the waste heat in order to maximise energy and carbon benefits.

Planningissues Traffic
TT facilities may be served by large numbers of heavy goods vehicle with a potential impact on local roads and the amenity of local residents. It is likely that the site layout/road configuration will need to be suitable to accept a range of light and heavy vehicles. Emissions/Health Effects The major emission from a plant with energy recovery is the release of flue gases from the combustion of the syngas or residual solid. The clean-up required for the flue gases is dependent on the process from which they have been generated. One of the main benefits claimed by manufacturers for pyrolysis and gasification plant is that emissions of pollutants are lower than those from conventional incineration. Entrained (fine) particles in the syngas can either be removed before or after combustion depending on the treatment process and combustion technology employed.

Planning issues A further solid residue that is produced is from abatement plant used to clean- up the flue gases from the combustion process. Both of these solid streams are hazardous and must be disposed of appropriately. Often they are combined as they are removed during the same stage of the flue gas clean-up. Dust / Odour Any waste management operations can give rise to dust and odours. These can be minimised by good building design, performing all operations under controlled conditions indoors, good working practices and effective management undertaken for dust suppression from vehicle movements. Flies, Vermin and Birds A TT processing is unlikely to attract vermin and birds due to majority of waste throughput and operations being completely enclosed in buildings. However, it is possible that flies could accumulate, especially if they have been brought in during delivery of the waste. Effective housekeeping and on site management of tipping and storage areas is essential to minimise the risk from vermin and

Planning issues other pests. In some operations waste heat from the process may be used to bring temperatures in fresh input waste to levels above which flies can live. The use of RDF as a feedstock would reduce this issue relative to raw waste. Noise The main contributors to noise associated with TT are likely to be: vehicle movements / manoeuvring; traffic noise on the local road networks; mechanical processing such as waste preparation; air extraction fans and ventilation systems; Litter Any waste which contains plastics and paper is more likely to lead to litter problems. With TT litter problems can be minimised as long as good working practices are adhered to and vehicles use covers and reception and processing are undertaken indoors. steam turbine units; and air cooled condenser units.

Planning issues Visual Intrusion
Visual intrusion issues should be dealt with on a site specific basis and the following items should be considered: Effect on landscape; removal of items such as trees or undertaking major earthworks Site setting; is the site close to heritage buildings, conservation areas or sensitive viewpoints Existing large buildings and structures in the area The potential of a stack associated with some air clean up systems for mixed waste processing operations may impact on visual intrusion Use of screening features (trees, hedges, banks etc); and The number of vehicles accessing the site and their frequency Public Concern Public concerns about waste facilities relate to amenity issues (odour, dust, noise, traffic, litter etc). With thermal based facilities health concerns can also be a perceived issue.

Table 4. Land requirement
Size and Land take Table 4 shows the land area required for the building footprint and also for the entire site (including supporting site infrastructure) for examples of thermal processes.

References Vesilind, P. A., Worrell, W., and Reinhart, D. (2002). Solid waste engineering. Brooks/Cole Thomson Learning, California, United States Pichtel, J. (2005). Waste management practices. Municipal, hazardous and industrial. Taylor & Francis Group, Boca Raton, United States

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