HSE 1101 Recycling of home and garden pesticide containers 3 Incineration There are a large number of waste incinerators in the UK, ranging from small laboratory incinerators to large operations that burn household waste (Defra 2007). Incinerators burn waste at very high temperatures (> 850 °C) which turns the waste to ashes, flue gas and heat reducing the initial volume of the waste by ~80-85%. The heat can be used to recover energy in form of heat or electricity, which is called Energy from Waste (EfW) or Waste to Energy (WtE). Incineration produces two forms of solid residue – fly ash, which is fine particulate matter carried with flue gases, and bottom ash, which falls from the fire-grate. They constitute, between them, about one quarter to one third of the total pre-combustion weight of waste. Flue gas must be cleaned of gaseous and particulate pollutants before being released to the atmosphere. Fly ash or air pollutant control residues (APCR) are disposed of as hazardous waste to landfills or other treatment facilities. Bottom ash is either disposed of as non-hazardous waste and goes to landfill after metals (mainly ferrous metals) have been recovered or recycled. Additionally waste water is produced as part of the pollution control process. 3.1 The incineration process Waste delivery and raw materials handling Different types of waste (depending on the plant permit) are delivered into the tipping hall by appropriate vehicles. The delivery vehicles are weighed on entry into the site, after which they tip their load into a capacity bunker. The vehicles are re-weighed on exit to calculate the amount of waste delivered to the site. Waste types normally include municipal solid waste (MSW), non-hazardous commercial, industrial or trade waste, but also small amounts of hazardous wastes. The tipping hall is operated under negative pressure to minimise escape of odours, dust or litter. The vehicles tip into a waste storage bunker from where the grab cranes mix the waste in the bunker to obtain a more controlled calorific value and to remove any unsuitable items. Then the grab cranes load the waste into a hopper from where it is pushed into the incinerator by hydraulic rams or falls by gravity onto the inclined rocking grate. In some plants the waste might be lifted using mechanical shovels into the feed hopper. Although less common, an incineration plant can also have a waste separation area where waste is sorted by size. In this case different waste fractions are further sorted and collected for processing into refuse-derived-fuel (RDF), or compost, or for recycling elsewhere; ferrous metals are removed by a magnetic separator and stored in a 'ferrous metals' area. Non- ferrous metals are removed by a separator and stored in a 'non-ferrous metals' area. Dense plastics will be separated off and stored for recycling. Combustion unit and boiler The waste is burned on a grate, with preheated air being injected above and below the grate. Combustion air is drawn from the tipping hall and boiler hall to reduce odours and dust levels in these areas and fed to the furnace via an air pre-heater. Burners, mainly fired on gas oil or low-sulphur diesel, are installed to maintain temperatures above the 850 °C threshold. The secondary air is drawn in part from re-circulated flue gas in order to reduce the formation of oxides of nitrogen Ammonium hydroxide can be injected into the furnaces to reduce emissions of nitrogen oxides (this technique is known as selective non-catalytic reduction or SNCR). The hot gases are maintained at a minimum temperature of 850 °C for 2 seconds in the presence of excess oxygen in the combustion chamber. The oxygen concentration and the 1 HSE 1101 Recycling of home and garden pesticide containers temperature should be carefully controlled to ensure effective combustion and to minimise the formation of pollutants, including dioxins. Residues/ash handling system Burnt out bottom ash residues are discharged from the lower end of each grate into a water- filled ash discharger, where it is quenched. The bottom ash is transported by moving belts into dedicated bunkers. Ferrous metals are removed from the bottom ash and then recycled. The bottom ash is removed from site for disposal or processed into an approved aggregate material e.g. for road building and construction. Residues from the flue gas treatment process are discharged in an enclosed system into e.g. double skinned heavy duty bags prior to removal from site for treatment and disposal. Flue gas treatment/air pollution control (APC) equipment Flue gases pass from the boiler to the gas cleaning equipment. The cooled gases enter a reaction chamber where lime dust and activated carbon are injected to neutralise acid gases and absorb (primarily) dioxins, volatile organic compounds (VOCs) and mercury. Nitrogen oxides (NOx) abatement can be achieved by the use of both flue gas recirculation (FGR) and selective non-catalytic reduction (SNCR) using ammonium hydroxide. The exhaust gases and reagent particles are then filtered in a fabric or bag filter to remove particulate matter and other pollutants. The filters are regularly cleaned, and the collected end product is stored appropriately in closed containers. The APC residue is disposed of in a suitably- licensed landfill site. The cleaned gas then discharges to atmosphere via a stack/chimney. Continuous emission-monitors analyse the exhaust gases from the chimney to include particulates, sulphur dioxide, oxides of nitrogen, carbon monoxide, hydrogen chloride, TOC and ammonia. Energy recovery Heat from the burning of the waste is used in the heat-recovery-boiler to raise steam which, in turn, is used in the steam-turbine-driven-alternator to generate electricity which is used for powering plant auxiliaries and the surplus is exported to the national grid. Some plants also have the capacity to export heat, in the form of high pressure hot water, to e.g. local factories. 3.2 Operating incineration plants and estimated waste incineration volumes in the UK Based on information available on the internet and on annual performance reports, 24 operational EfW incinerators in England were identified excluding incinerators in planning or decommissioned incinerators1. It has to be noted that the number of operational municipal incinerators in the UK is constantly changing due to building and commission of new incinerators, decommissioning of old incinerators as well as closing/re-opening of existing incinerators and therefore reliable information is difficult to obtain. Reports from Defra 2007 and Tolvik consulting 2011 therefore show a discrepancy of operating incinerators (see Table 2 and Table 3). Table 1 provides an overview of the identified incinerators and the volume of waste incinerated each year, also detailing the volume of residues based on the latest available annual performance reports. Whilst the data are now a little dated, they still provide a good estimate of total waste volumes incinerated as well as produced residues by incinerators in the whole of the UK. Based on this data we assume that a total of ~4,325,021 Tonnes of 1 http://ukwin.org.uk/resources/table/; http://ukwin.org.uk/resources/incinerator-reports/; https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/181825/pb13889- incineration-municipal-waste.pdf.pdf 2 HSE 1101 Recycling of home and garden pesticide containers waste are incinerated in the UK per annum leaving behind a total of 127,822 Tonnes of air pollution control residues (APCR) and 717,157 Tonnes of bottom ash for landfill or additional waste treatment. There has also been a report by Tolvik consulting (Tolvik consulting 2011) evaluating the performance of the 19 EfW plants operated in England and Wales. For the years 2008 and 2009 the volume of incinerated waste by these plants are given in Table 2. According to Tolvik’s data 3,266,512 and 3,490,079 tonnes of waste have been incinerated in England and Wales in 2008 and 2009, respectively. For all the analysed EfWs, Tolvik report that municipal solid waste (MSW) was the principle feedstock (~98% of processed waste being MSW). Tolvik further state that, of the 16 facilities analysed, 12 reported bottom ash tonnages of between 19.5% and 22.0% of total waste throughput. Half the facilities reported that the bottom ash was recycled, whilst for the rest, where it was landfilled in 2008, nearly all the annual reports pointed to plans to move to bottom ash recovery. Similarly, for Air Pollution Control (APC) Residues, the figures reported were all in the range of 2.5 to 3.8% of waste feed. All reported ultimate landfill disposal although some detailed the pre-treatment provided. Table 2 shows incinerators and waste incineration capacities (tonnages per year) for the UK and Table 3 gives output values for solid residues and gaseous emissions in % from incinerator technologies, both tables taken from Defra (2007). 3 HSE 1101 Recycling of home and garden pesticide containers Table 1 Operational waste incineration plants in the UK. Plant Type Operator Hazardous Non-hazardous waste Waste inc. Year waste (tonnes) ACPR (tonnes) bottom ferrous metals ash metals recov. recov. (tonnes) (tonnes) (tonnes) Allington EfW Kent EnviroPower Ltd 15619 13189 4812 1861.15 132540.63 2008 Baldovie (Dundee) EfW Dundee Energy Recycling Ltd (DERL) 120000 capacit y Bolton EfW Viridor Ltd 2457.86 18724.61 1861.15 84939 2009 Chineham EfW Veolia 2904 20593 1662 98562 2011 Colnbrook (Berkshire) EfW Grundon Waste Managem. Ltd & Viridor 383716 2010 Coventry EfW The Coventry & Solihull Waste Disp. 7519 52565 7925 245187 2009 Comp. Ltd Dudley EfW MES Environmental Ltd 3286 1288 91362 2011 East Kent HTI Augean waste network 10000 capacit y Eastcroft (Nottingham) EfW WasteNotts Ltd 4898 30446 2915 159268 2011 Edmonton (London) EfW LondonWaste Ltd 16478 86301 16478 521246 2008 Ellesmere (Cheshire) HTI Veolia 10000 capacit y Fawley HTI Pyros Environ.