A burning question

With depleted oil stocks in the North Sea meeting less of our energy needs, the UK has been a net importer of gas for the past five years. Supplies are at a disturbingly low level. Average reserves are sufficient for about two weeks – nine times less than in Germany. Equally worrying is that a measured overhaul of the infrastructure of nuclear and coal-fired power stations is now too late to avoid demand for electricity outstripping supply by 2014. The one thing we do have in abundance is waste, so why not make good use of it?

Hitherto, support for recovering energy through burning waste has been lukewarm, largely shaped by an antipathy to incineration as a means of waste disposal. Basically, no one wants to live next door to a bonfire.

Other European countries, in particular those in Scandinavia, have demonstrated fewer qualms. According to the British Plastics Federation (BPF), Denmark, with a population of barely five million, sports one-third more energy-from-waste (EfW) plants than the UK. The UK recovers less than 10% of municipal waste through incineration in its 24 EfW plants.

BPF director general Peter Davis holds the government accountable for failing to grasp EfW opportunities. “They’ve been more focused upon increasing the recycling rates. That has been effective, and as far as plastic goes we’ll be up to the levels across the rest of Europe within a year or so.”

Used plastic packaging is central to the debate. “The calorific value of plastic is greater than that of coal,” says David Tyson, director of the Packaging and Films Association (PAFA). “One of the great concerns in the UK has been that if we grow energy from waste, we’ll then divert good recyclable material. That hasn’t happened in Europe, where recycling and incineration rates are equally impressive.”

Government recognition
The government’s ‘Waste Strategy for England’ white paper, published two years ago, identified an annual volume of 100m tonnes of waste per year generated by households, industry and commerce. While the main focus of the paper was to reduce landfill use through increased recycling and composting, there was a tacit acknowledgement that EfW had a role to play. A target was set to transform 25% of municipal waste into energy by 2020.

Key to transforming public opinion is convincing people of the safety of modern incinerators. One-time inefficiencies have been largely eliminated through stringent EU directives. While a small element of residual ash is deemed to be toxic, the vast proportion goes to construction or road aggregate. It is estimated that UK EfW plants contribute 0.8% of the total regulated dioxin emissions, compared with domestic heating which produces around 19.4%, and the iron and steel industry at 13.1%.

“Newer incineration facilities are energy efficient and conform to EU directives, and older ones can be easily upgraded. Organisations such as Friends of the Earth have a very different attitude abroad, where there is a strong acceptance of energy from waste,” says Davis.

In the meantime, newer technologies, notably gasification and anaerobic digestion, are coming on-stream.

Energos, part of UK-based sustainable energy technology company ENER-G, uses its patented gasification technology, an advanced two-stage thermal treatment process that converts residual, non-recyclable waste into a gas by using the heat of partial combustion to release the hydrogen and carbon within the waste.

The UK’s first gasification plant, just opened on the Isle of Wight, draws its 30,000 tonnes of feedstock locally and is set to generate around three megawatts (MW) of electricity a year. This was previously supplied from the mainland. Energos managing director Nick Dawber says: “The project has made use of existing infrastructure and equipment, including boilers, steam turbine, and flue-gas cleaning equipment from a former incineration plant. It is built around an existing materials recovery facility (MRF). The track record for all operational plants across Europe and Scandinavia confirms that dioxin emissions are typically 1% of the EU safe-limit.”

Plasma gasification, which uses advanced alkaline fuel cells to convert hydrogen into electricity, is the next-generation technology to look out for, says Peter Jones at Waste2Tricity, which turns solid municipal waste into electricity. “What we need to achieve is the lowest CO2 emissions per tonne of processed waste and the highest energetic conversion rate. Our system is capable of matching current electricity generating costs of around three pence per kilowatt-hour – half of what it would be via nuclear or wind-powered alternatives. It also eliminates tar and toxic gases as well as reducing residual ash to below 5%.”

Gains must be set against initial set-up costs. A 250,000-tonne plant proposal going before the London Waste Recycling Authority would cost around £150m to build, in order to generate 25MW per year. This represents a capital investment per megawatt of about double that estimated for nuclear (£3m per MW).

Garnering interest
Air Products, which supplies industrial gases and equipment, and alternative energy firm Alter NRG have already indicated an interest in investing in the technology. Jones hopes it will provide an EfW solution at landfill-sited MRFs throughout the country, incorporating a significant proportion of the packaging sector’s 10-15% contribution to the national waste pool.

Were compostable film to take hold, anaerobic digestion could prove to be a viable EfW alternative. “A lot of our product ends up in deli containers or clam-shells. It isn’t practical to clean those things, but you can put the scrap food and the packaging into an anaerobic digester and reprocess the lot,” says Eamonn Tighe, business development manager at NatureWorks, which makes PLA.

While the UK weighs its options, other countries are forging ahead. “In China, they’re building four million anaerobic digestion plants a year at household level and using the resultant bio-gas for cooking purposes,” says Michael Chesshire, technical director at anaerobic digestion firm Biogen. “Feedstock that’s characterised by a high moisture content is ideal.”
Anaerobic digestion, despite its lengthy processing cycle and limited range of feedstock, gets the most positive nod from the green lobby. Thermal-based alternatives are less well received.

Why bother with them anyway, asks the UK Without Incineration Network (UKWIN) national co-ordinator Shlomo Dowen. “When you get to the bottom of the waste hierarchy, then landfill is actually a better option environmentally than incineration. For plastic, which doesn’t emit methane, it’s effectively a form of storage. I don’t accept that we’re running out of space for well-managed landfill; that’s a myth. What happened was they determined the availability of landfill at a given moment and took that to be a once-and-for-all limit. In reality, new holes are being dug all the time but aren’t being added to the capacity.

“If all biodegradable material was used for fuel or anaerobic digestion, then the remaining inert material could be safely stored under or above the ground in appropriate containers and available to be used as a future resource.”
As the global population grows its energy demands will rise accordingly. One of the few resources that will actually grow with the population, rather than be depleted by it, is waste. So while opinions continue to be divided on the subject, it is unlikely to run out of steam for some time to come.

HOW A GASIFICATION EFW PLANT OPERATES

• Energos has five facilities in Norway (a sixth plant is currently under construction); one facility in Germany, and one in the UK (Isle of Wight). A typical plant generates 8MW of electricity from 80,000 tonnes of waste, and would cost £40m to build over two years
• A gasification plant incorporates a two-stage thermal conversion process controlled and monitored throughout by a proprietary software system
• Fuel used in an Energos plant is pre-treated waste, which is delivered to the energy plant, unloaded in the fuel bunker (1) and delivered to the gasification unit by overhead crane (2)
• Drying, pyrolysis and gasification of the fuel is carried out in the primary chamber (3)
• The syn gas (a synthesis gas mix containing carbon monoxide, carbon dioxide and hydrogen) generated in the primary chamber is transferred to a separate secondary chamber (4) where final high-temperature oxidation takes place
• The heat recovery steam generator (5)
that recovers the energy from the flue-
gas is connected downstream of the high temperature oxidation unit  
• The energy utilisation system is project specific and designed to satisfy the requirements of the energy user
• The flue-gas then enters the flue-gas cleaning system which consists of a bag-house filter (6); a storage silo for lime and activated carbon (7) and a filter dust silo (8)
• The bottom ash (approximately 15% of input waste) is discharged from the gasification unit at the end of the grate (9)
• According to Energos, it takes between 20-30 minutes for the waste to enter the reactor and exit as ash into the quench system

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