Puzzling over incineration
As we look to manage our waste problems and meet landfill diversion targets, there are now many technological options at our disposal. One that’s been around (and hotly debated) for ages is incineration. Libby Peake finds out if it can fit into the modern waste management puzzle
Before we get started, let’s clear something up: what exactly does ‘energy from waste’ mean? It’s a slippery fish – normally used as a euphemistic synonym for incineration. But energy can be extracted from waste through all sorts of technologies – anaerobic digestion, pyrolysis, gasification and so on. So, for the purposes of this article, we’re simply going to call technologies by their proper names – regardless of potentially negative implications.
Long before the phrase ‘energy from waste’ confused the incineration debate, incinerators were known by an altogether different name with even greater negative connotations: destructors. The world’s first mass-burn destructor for waste disposal was designed by Stephen Fryer (yes, Fryer) and built in Nottingham in 1874. Apart from relatively uncontrolled tipping, this was the main form of waste management in much of Victorian Britain. Items were simply fed into the furnace to be destroyed. Even in those early days, some destructors produced electricity, but little recycling or pollution mitigation made the process efficient.
Incineration technology has, naturally, moved on since then. There are several ways in which to combust solid waste with the aim of generating power – in theory after recyclables have been removed – with increasingly exotic names like bubbling- and circulating-fluidised bed incineration. By far the most common way to burn municipal solid waste, however, is moving or roller grate incineration. Richard Kirkman, Head of Technology at Veolia Environmental Services, which operates six of the 19 municipal waste incinerators in England and Wales, claims it’s “the most developed technology and gives probably the most efficient burnout”. In this technique, an oscillating or tubular rolling steel grate turns the waste as it goes into the furnace to ensure the rubbish is completely burnt. Even so, not everything is destroyed: between 20 and 30 per cent of the weight of waste processed remains as bottom ash, which is commonly reused in aggregates and building materials, though some still heads for landfill.
The process of then generating electricity is relatively simple, as Kirkman explains: “We incinerate the waste and then the hot gases come off and go through a boiler, a metal box where all the walls have water in them, and that boils up, makes steam, goes into the turbine and produces electricity. That part of the process is exactly the same as a coal-fired power station, except we’re using waste instead of coal.”
The next steps in the incineration process differ a great deal from the coal-burning process, largely because of the 1989 EU directives on air pollution from new and existing incinerators. UK incinerators were all either shut down or upgraded in the 1990s and are now “really heavily regulated” in comparison to other power stations according to Kirkman. After performing its power-generating feat, the cooled flue gas, which at that point contains pollutants like acid gas and heavy metals, usually goes through a ‘gas scrubber’. Kirkman explains: “We take lime, which is a chalky white powder, mix it with water and then spray that in a tank through a nozzle, which atomises it. The gas passes through that very fine spray, which neutralises and captures the acids.” Organic compounds, on the other hand, are dealt with by ‘activated carbon’: “The carbon has been treated in such a way that a fine speck of carbon would have several centimetres squared of surface area. It’s got lots of little holes that go into more and more little holes. When you put it into the gas, all the organic compounds like dioxins and PCBs go inside the holes and are locked there,” says Kirkman.
At this point, the milky lime mixture will be dried by the hot gases and will drop out as solid residue and the gas then passes through a ‘bag filter’, a box with steel cages covered in fabric socks that capture remaining particulates. The air pollution control residue / fly ash from these processes, which weighs the equivalent of two per cent of the incoming waste, is classed as hazardous waste and must either undergo further treatment or be stored away where it can never again see the light of day (or feel the rush of water or cracks in soil).
Modern incinerators must comply with emissions standards from the 2000 Waste Incineration Directive, which was transposed into UK law in 2007. Many pollutants – like nitrous oxides, volatile organic compounds and particulates – are continuously monitored with standard laboratory tests on samples and devices like dust monitors, which fire laser beams across chimney stacks to determine particulate content based on loss of light. Other pollutants, such as dioxins and heavy metals, however, are only monitored twice a year.
Because of all this regulation, a Defra spokesperson claims we’re safe to breathe (and eat and live in general) around modern incinerators: “The latest scientific evidence… concludes that while it is not possible to rule out adverse effects completely, any potential damage from modern, well-run and regulated incinerators is likely to be so small that it would be undetectable.”
So far, so good – safety checks protect people and the environment and incineration generates electricity to boot – it seems like the perfect solution to our waste and energy crises. So why is there so much opposition to even these technologically-advanced, rigourously-monitored incinerators?
Well, health and environmental concerns certainly come into it and the idea that ‘it is not possible to rule out adverse effects’ doesn’t inspire much confidence. Indeed, despite the rigours of monitoring, anti-incineration campaigners point out that pollutants do sometimes slip out. Waste campaigner Keith Kondakor recently obtained Environment Agency documents showing two incinerators in the West Midlands, both operated by MES Environmental, have exceeded dioxin levels on multiple occasions. Dioxins are highly unstable, fat-soluble compounds that are suspected carcinogens and impact on development – a dioxin was the principal component of Agent Orange, employed with such disastrous consequences in Vietnam. Dioxins are considered ‘safe’ up to a level of 0.1 nanogrammes per cubic metre (ng/m3), and flue gas normally contains just 0.02 or 0.03 ng/m3 of dioxins. The incinerator at Dudley exceeded the limit in four of eight tests conducted in 2008 and 2009, though, and the plant in Wolverhampton had a reading of 0.6041 ng/m3, more than six times the legal limit.
When asked what might cause these violations, Kondakor explains: “It’s basically because you’ve got combustion at the wrong temperature. They run incinerators very hot – 850°C – so that if any dioxins form they instantly break down. So, if the rate of feeding is wrong or the type of waste – if suddenly the calorific value of the waste drops – the temperature in the combustion chamber can drop.”
A further concern comes from the inefficiency of the incineration process, as a great deal of embedded energy is lost through waste heat; the electrical efficiencies of the process are between 15 and 25 per cent according to environmental consultancy AEA, so each tonne of waste generates between 500 and 750 kilowatt hours (kWh) of electricity, depending on composition. By comparison, coal-fired power plants have electrical efficiencies of 30 per cent (still nothing to brag about) and coal has a greater calorific value, so such stations produce around 2,000 kWh per tonne.
Of course, if plants are operated with combined heat and power (CHP), efficiency levels rise, up to 79 per cent according to AEA. Unfortunately, CHP isn’t a viable option for most UK incinerators because heat, unlike electricity, must be used locally. As AEA’s Practice Lead on Waste Management and Resource Efficiency Dr Adam Read explains: “CHP can be really difficult to integrate with existing local energy systems. You can find yourselves having to dig up pavements left, right and centre. So, it’s quite disruptive, it’s quite costly, and given the UK situation, which has always been about cheap landfill, it doesn’t tend to be very good value for money.” In 1994, for example, Veolia built South East London Combined Heat and Power (SELCHP) but still hasn’t converted any waste to heat as the required pipe network doesn’t exist, though Kirkman insists “we’re on the brink”.
The government’s Renewable Heat Incentive could make CHP more viable, but even then it would still only be a realistic option for new housing and industrial estates and, as independent waste consultant Peter Jones points out: “Any new housing estate – if it’s built to the appropriate standards – will not want heating or cooling because it will be self-sufficient. Therefore, the idea of having heat networks to houses is not the right way to go about it.”
Furthermore, though incinerators stand up well against coal-fired power stations in terms of their CO2 emissions, they certainly aren’t climate friendly. The Eunomia report ‘A Changing Climate for Energy from Waste?’ found that incinerators that only generate electricity emit 510 grammes (g) of CO2 equivalent (CO2e) for every kWh of electricity, which is better than coal-fired power stations (835gCO2e/kWh), but worse than gas-fired stations (383gCO2e/kWh) and doubtless dismal compared to other ‘renewable’ sources.
What’s more, in line with current practice, the figure for incineration omits biogenic carbon, in theory because biomass absorbs as much CO2 in its life as it emits in its destruction. As Friends of the Earth’s Senior Campaigner on Resource Use Dr Michael Warhurst points out, though, this approach is problematic because “the atmosphere doesn’t know the difference between biogenic and non-biogenic carbon”. As we move into a world where carbon becomes the new currency, where, as Jones notes, “you’ll want to have the lowest exposure to carbon tradable permits or carbon taxation”, incineration’s carbon footprint will be a further black mark against it.
For the time being, incineration remains a relatively popular option, especially where large PFI deals are concerned, because it’s viewed as a mature, low-risk, bankable technology able to handle many waste streams. Warhurst suggests it’s also popular because: “It’s perceived as easier to spend lots of money buying something big which will allegedly solve your problems, than it is doing a lot of smaller things which will be less expensive and solve your problems more effectively.” Incinerators are indeed large and expensive: a 200 kilotonne per annum (ktpa) plant (which could take the residual waste created by nearly 700,000 people at today’s rates of waste generation) costs over £100 million to build and charges gate fees of £58.5 per tonne based on 2007 Defra figures. A similarly sized anaerobic digester (which could only take biomass, granted) would cost a fraction of the price (£28.8 million for a 150ktpa facility) and only charge £37.9 per tonne of waste in gate fees.
Nonetheless, more than 60 potential incinerators around the country (some as big as 600,000ktpa) have been mooted in some way by local authorities, central government or the media, according to the UK Without Incineration Network. And some authorities are misestimating waste levels in business cases for PFI deals. According to WasteDataFlow statistics, municipal waste arisings peaked in 2004/05 and falling rates have recently been helped along by the recession. However, when it comes to planning applications for incinerators, Warhurst says: “What we’ve seen in recent years is a consistent use of assumptions that waste will grow at three per cent a year.” Consequently, authorities procure bigger incinerators than they need and must then feed them a consistently high level of waste throughout their 25-year lifespans.
While some claim shortfalls can be countered by adding commercial waste, others are concerned the need to feed incinerators could crowd out recycling and other actions higher up the waste hierarchy. Warhurst says councils planning incinerators often project a maximum of 50 per cent recycling and as a result, “will encourage recycling up to a point, but won’t want to do it beyond that because they’ll need to generate waste to fill the incinerator”. He points to Denmark as an example of this – the country is heavily dependent on large incinerators and some regions have recycling rates well below 30 per cent: Hovedstaden – the ‘Capital Region of Denmark’ – recycles just 21 per cent of its waste and burns 77 per cent.
Some worry this is already happening here: “Quite a lot of people say that down in Kent there was a plan to do a really substantial expansion of furniture reuse and that was called off because the new incinerator at Allington required waste,” Warhurst claims.
The fact that furniture that could be reused is being fed into an incinerator is, of course, a great shame. These facilities were aptly titled the first time round as destructors – they necessitate a linear system of resource extraction, production, consumption and disposal, and though energy is recovered, some of the world’s finite resources are destroyed in the process. Indeed, some of the material types with the highest calorific value in an incinerator are plastics and biomass, which, for the most part, could and should be recycled into more plastic or compost / digestate (and energy), et cetera.
As Adam Read points out, though: “The public now believe that recycling is the answer to everything. Well, it’s not. It’s the answer to about 60 per cent of our problems. The other 40 per cent needs something else.” While some might contest the figures – zero wasters and the governments of Wales and Scotland spring to mind – the point remains that for the foreseeable future there will be some residual waste left after organics and recyclables are removed. Too many hungry incinerators won’t fit in the waste management puzzle, but as we piece our practices together, those other (modular) technologies that generate energy from waste might just slot into place. Dig into our next issue to find out how they measure up…