NNFCC     The Bioeconomy Consultants    Energy from Waste:The benefits of upgrading household   waste before energy recove...
INEOS Bio plan to generate                                                                low carbon electricity and      ...
Incineration or             plasma gasification                                                                          S...
MSW                                                   MSW                           rejects                               ...
and pyrolysers need a fuel with a              GHG balances of different MSW toconsistent particle size and a moisture    ...
technology, MHT returns up to 40 percent of the energy present in each tonneof MSW, compared to around 33 per cent        ...
implications of waste pre-treatment.        same tonnage of material, which may beProcessing waste into SRF or RDF can    ...
By 2020 energy from wastecould generate more than3TWh of electricity in the UK5
to a moisture content of just 15 to 18 per   •	 Smaller ash handling and holdingcent for SRF3,4.                          ...
per MWh, although this may not alwaysbe the case since the lower heating value                                            ...
Energy from Waste Briefing Page 10
NNFCC is a leading international consultancy with expertise on theconversion of biomass to bioenergy, biofuels and bio-bas...
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NNFCC briefing document. energy from waste the benefits of upgrading household waste before energy recovery

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Most businesses now recognise waste as a valuable resource but which end-of-life treatment offers the best returns for the environment and for the economy? This essential briefing explores the benefits of producing refused-derived fuel and solid-recovered fuel for use in energy from waste facilities.

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NNFCC briefing document. energy from waste the benefits of upgrading household waste before energy recovery

  1. 1. NNFCC The Bioeconomy Consultants Energy from Waste:The benefits of upgrading household waste before energy recovery September 2012
  2. 2. INEOS Bio plan to generate low carbon electricity and fuel from pre-treated MSW in the Tees Valley, UK Image: © INEOS BioW aste has become a valuable resource for producing energy but which end-of-life energy recovery option offersthe best returns for the environment and for the economy?As we move towards a zero waste temperatures to produce heat andeconomy, waste managers are having power. But this can be inefficient,to look for alternatives to landfilling particularly if the feedstock has a highwaste. Where waste cannot realistically moisture content.be prevented, re-used, or recycled, Alternatively, we can “partially” upgraderecovering the energy stored in waste MSW to refuse derived fuel (RDF) orstarts to become an environmentally and “fully” upgrade it to solid recoveredeconomically attractive option. fuel (SRF) by mechanically separatingEnergy recovery can be particularly the recyclates from the waste anduseful in treating mixed waste streamslike municipal solid waste (MSW). TheUK alone creates around 30 million Useful definitionstonnes of MSW every year1, and thanksto its high levels of organic matter – like MBT - Mechanical Biologicalpaper and food waste – it could have Treatment; a mechanical sorting process followed or preceded byenormous value as a source of low a biological treatment, such ascarbon energy. composting or anaerobic digestionWe can recover energy from waste MHT - Mechanical Heat Treatment; aby simply incinerating it at high thermal treatment using autoclaving followed by mechanical sorting
  3. 3. Incineration or plasma gasification SORTED WASTE WASTE ANAEROBIC DIGESTION, Material Segregation COMPOSTING Sterilisation in Autoclave Material Segregation PYROLYSIS, GASIFICATION, REMEDIATION, COMBUSTION Waste management alternatives to landfillbiologically or thermally treating it. This MBT uses mechanical sorting to separatefuel can then be used to create a range of recyclates from the MSW, this is typicallyproducts at high conversion efficiencies. followed by one of three processes:This briefing paper explores the benefits • Aerobic decompositionof producing RDF and SRF for use in (Composting)energy from waste facilities. • Anaerobic digestionPre-processing of waste • Bio-dryingA range of processes exist for upgrading Aerobic decomposition and anaerobicMSW, from simple sorting and shredding digestion use organisms to break downthrough to more complex mechanical the organic waste. This helps to stabilisebiological treatment (MBT) and the waste, reduce its volume and createmechanical heat treatment (MHT). useful sorted fractions such as compost Energy from Waste Briefing Page 2
  4. 4. MSW MSW rejects Initial Shredder rejects 3.6% scalping 3.6% Co2 3.1% Bio-drying H2o 32.2% autoclave Densimetric Densimetric fe metals seperation seperation Metal 5.4% Trommel seperation non-fe metals 1.0%fe metals Magnetic Magnetic fe metals 1.4% seperation seperation 3.5% Heavy Inerts Density Density residues 6.4% seperation seperation 12.2% non-fe non-fe eddy current eddy current metals metals light seperation seperation 0.5% 0.5% fibre 61.5% autoclave residues 9.9% pelletiser Inert residues 8.6% Srf 46.6% MBT mass balance example MHT mass balance example in the case of aerobic decomposition, waste, but at present isn’t widely used in and digestate and a combustible gas the treatment of MSW. – known as biogas – in the case of MHT processes produce dry recyclates, anaerobic digestion. a residual fraction and a fibre similar Bio-drying – a variation of aerobic to SRF. A typical MHT mass balance is decomposition that uses natural process illustrated above (right). heat to dry rather than fully stabilise waste – is an approach used to produce Why pre-treat waste? RDF and SRF. A typical mass balance for While pre-treating waste to RDF or MBT with bio-drying is shown above SRF is usually not needed for mass (left). burn incineration (MBI), it can add considerable value to waste streams In contrast, MHT processes use steam and is often a requirement for or direct heat to treat waste. MHT more advanced energy conversion processes typically incorporate the use technologies, like gasification and of autoclaves – devices used to sterilise pyrolysis. and break down organic matter. This additional pre-processing is Autoclaving is common in other normally necessary because gasifiers industries, like the treatment of medical
  5. 5. and pyrolysers need a fuel with a GHG balances of different MSW toconsistent particle size and a moisture energy technologies. They compare:content below about 30 per cent. • MBI with electricity generation orHowever, this isn’t always the case, for combined heat and power (CHP)example ‘plasma’ gasifiers can process production using untreated MSWuntreated MSW. • MBT (bio-drying) with electricityPre-treating waste with MBT or MHT to generation in a co-fired power plantmake RDF or SRF can offer a number of or CHP production using SRFbenefits when used in conjunction with • MHT with electricity generationenergy recovery. These include: in a co-fired power plant or CHP• Reduced greenhouse gas (GHG) production using SRF emissions, as well as fewer heavy The energy and fuel use for the three metals and less dust in the fly ash2 pre-treatments are illustrated in the• Improved downstream efficiency of table below. This shows that the energy energy recovery demands of MBT and MHT processes are• Increased recycling potential considerably higher than those of MBI.However, the energy demands and However, to appreciate the overall pre-outputs of MBT and MHT processes will treatment benefits, displaced energyvary according to a number of factors, demand from recovering recycledincluding the composition of the waste, materials and downstream energyprocess design and the downstream user conversion of the pre-treated wasterequirements, such as biogenic content must be considered.and calorific value. According to Papageorgiou et al.3 if wePapageorgiou et al.3 is one of the few take into account whole system or lifestudies that compares the energy and cycle energy credits for each conversion Pre-treatment energy demand and fuel use Input (kWh/tonne MBI MBT MHT of waste received) Electricity 4 80 24 Diesel 1 10 10 Natural Gas 0 0 177 Total 5 90 211 Energy from Waste Briefing Page 4
  6. 6. technology, MHT returns up to 40 percent of the energy present in each tonneof MSW, compared to around 33 per cent MBI with electricityfor MBI. MBT with electricity (co-firing)Greenhouse gas emissionsThe GHG emissions saved by pre- MHT with electricity (co-firing)treating waste depend on what energyprocess they are being used to displace. MBI with CHpTo date the evidence is inconclusive as MBT with CHpto whether pre-treatment saves GHGemissions compared to MBI, when the MHT with CHpenergy is recovered in a CHP plant.Although there may be some benefit -350 -250 -150 -50 50to using MHT as a pre-treatment. In Total GHG emissions (kg CO2 eqaddition, there is very little information per tonne of waste) for contrastingavailable to compare MBI to advanced energy from waste options3conversion technologies, which is anarea in need of further research. potential emissions savings seen when pre-treating waste by MBT or MHTHowever, there is evidence3 to suggest followed by energy recovery will dependthat when displacing coal in a power on the market for recyclates and finalplant there are significant advantages use of the SRF.to converting waste to RDF or SRF, asshown above right. If we consider a realistic scenario for the UK, where most MSW is incinerated,If there is no market for the recovered with smaller but increasing quantitiesmaterials such as ferrous metals, non- converted to SRF via MBT and MHT,ferrous metals and inerts like glass and significant GHG savings can be realisedash, waste pre-treatment can still reduce compared to straight incineration oflife cycle GHG emissions, although these untreated MSW3 when displacing coalsavings decrease by as much as 50 per and in some cases gas, assuming the SRFcent3. is used for energy production and the recovered materials are recycled.In contrast, if the SRF is landfilledrather than used for energy recovery, While GHG emissions are an importantGHG emissions for MBT or MHT will be social and political consideration, ithigher than MBI3. This shows that the is also valuable to consider the wider
  7. 7. implications of waste pre-treatment. same tonnage of material, which may beProcessing waste into SRF or RDF can desirable.also improve the combustibility of Alternatively, if it is more importantwastes in a number of other ways. to have a high organic matter content – perhaps for those looking to claimSometimes it is desirable to control renewable energy subsidies – theOrganic matterthe amount of organic matter present process can be modified accordingly.in the fuel. Organic matter has one ofthe lowest calorific values and highest Moisture contentmoisture contents in the slate of Before a fuel can be converted to energy,materials making up MSW. If we reduce all remaining moisture must be driventhe percentage of organic matter in the off inside the combustion or gasificationwaste stream, this will make energy reaction chamber.conversion more efficient. Hence, increased moisture levelsWe can achieve this by processing MSW represent increased efficiency losses.into SRF or RDF. The organic matter in In the case of gasification, some of thisRDF is typically less than 25 per cent by drying may need to be carried out beforemass, while in untreated MSW it can be the waste is introduced to the gasifier,as high as 50 or 60 per cent2. depending on the gasifier type.The improved calorific value allows MSW typically has a moisture content ofsmaller waste fuelled power stations to between 30 and 40 per cent, comparedproduce more electrical output from the Lakeside energy from waste plant Image: © Viridor Energy from Waste Briefing Page 6
  8. 8. By 2020 energy from wastecould generate more than3TWh of electricity in the UK5
  9. 9. to a moisture content of just 15 to 18 per • Smaller ash handling and holdingcent for SRF3,4. system is needed at incineration plants. This decreases capital costs,However, the fibre produced by MHT can albeit not greatly.contain as much as 50 per cent moisture,resulting in a low heating value. To use • Where batteries are removedMHT fibre as a fuel it normally needs to by upstream MSW processing tobe dried, preferably using waste heat. produce RDF or SRF, heavy metals levels (e.g. zinc, cadmium, mercury) in the recovered ashes and any flyAsh contentRemoving non-combustibles from MSW ashes will be reduced3.means that SRF and RDF have reducedash contents compared to untreated Acidic flue gasesMSW. MSW can contain around 20 to Per tonne, SRF contains more sulphur40 per cent ash content by mass2,4 while and chlorine than MSW. Hence, moreSRF and RDF contain around 10 to 20 sulphur dioxide and hydrochloric acidper cent by mass2,3,4. will be emitted when one tonne of SRF is burnt compared to one tonne of MSW.This compares more favourably to coaland woody biomass which have ash However, more energy will be producedcontents of 5 to 10 per cent by mass and from the SRF so on an acidic gases per1 to 2 per cent by mass, respectively4. MWh basis the SRF is cleaner. This means that SRF will typically have aThe reduced ash content of SRF lower acidification potential than MSWcompared to MSW means that lessheat is lost heating up the ash in thecombustion or gasification chamber.As a result more of the availablechemical energy is converted into usefulproduct such as electricity, resulting inincreased conversion efficiency.The reduced ash content of SRFcompared to MSW also provides thefollowing environmental benefits: Air Products are building the worlds• Lower fly ash emissions from the largest advanced gasification energy from waste facility in Teesside, UK - combustion process, which reduces due to be completed in 2014 smog potential and removal costs. Image: © Air Products Energy from Waste Briefing Page 8
  10. 10. per MWh, although this may not alwaysbe the case since the lower heating value Looking to the futurecan vary. To date energy from waste has not fulfilled its potential as a method forIf plant operators switch from MSW to material or energy recovery and hasSRF or RDF with a higher acid gas level been used more as a waste managementper tonne, care will need to be taken tool. But we are starting to see a shiftto ensure that emissions do not rise where the value of waste is being morebeyond permitted levels, regardless of widely recognised.whether the plant produces more netMWh of power per year. The end-of-life use of waste should conform, where possible, to the waste hierarchy, but where it cannot be practically re-used or recycled, energyMaterial consistencyMSW is a heterogeneous resource, both recovery is preferable to landfilling.in terms of its constituent materials andparticulate size; meaning it is composed The most appropriate technology toof particles of different shapes and sizes. convert waste to energy will depend on its intended end-use and the market forProcessing MSW into RDF or SRF will recyclates, but MBT and MHT can offerhave the effect of homogenising the significant environmental and economicmaterial and making it easier to burn or benefits over incineration.gasify consistently. Background information 1. Evaluation of Opportunities for Converting Indigenous UK Wastes to Fuels and Energy. Barker N and Evans L. 2009. NNFCC Report 09-012. 2. Analysis and comparison of municipal solid waste and reject fraction as fuels for incineration plants. Montejo C, Costa C, Ramos P and del Carmen Márquez M. 2011. Applied Thermal Engineering (31), pp. 2135-2140. 3. Assessment of the greenhouse effect impact of technologies used for energy recovery from municipal waste: a case for England. Papageorgiou A, Barton J R and Karagiannidis A. 2009. Journal of Environmental Management (90), pp. 2999-3012. 4. An integrated appraisal of energy recovery options in the United Kingdom using solid recovered fuel derived from municipal solid waste. Garg A, Smith R, Hill D, Longhurst PJ, Pollard SJ and Simms NJ. 2009. Waste Management (29), pp. 2289-2297. 5. UK jobs in the bioenergy sectors by 2020. McDermott F. 2012. NNFCC Report 11-025.
  11. 11. Energy from Waste Briefing Page 10
  12. 12. NNFCC is a leading international consultancy with expertise on theconversion of biomass to bioenergy, biofuels and bio-based products.NNFCCBiocentreYork Science ParkInnovation WayYorkYO10 5DGUnited KingdomTelephone: +44 (0)1904 435182Email: enquiries@nnfcc.co.ukWebsite: www.nnfcc.co.uk

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