Across Europe and, increasingly elsewhere, landfill has become a dirty composite word. Yet the power industry’s best efforts to turn rubbish into a resource have become mired in controversy. Can it convince a sceptical public that the combined goals of ‘zero waste’ and sustainability are worth keeping the waste-to-energy (WtE) dream alive? Chris Webb considers the options.

 

Chris Webb

French Europlasma develops, produces and markets waste processing/energy production solutions based on its proprietary plasma torch technology, and operates as a waste gasification power producer via its CHO Power company Source: Europlasma SA

Waste, rubbish, trash. Whatever you call it, it is a nuisance. Unless, that is, you call it a resource, which is precisely what the power industry has been calling it for four or five decades at least. But don’t mention incineration, or you are bound to succumb to an environmental trap that has frustrated the development of waste-to-energy – or energy-from-waste – since engineers first hit on the idea of a solution to the world’s growing mountain of waste and its equally impressive hunger for power.

It is why generating electricity from waste poses such a dilemma. Throughout the western world, the potential for WtE technologies is widely acknowledged as a key mitigating instrument for reducing landfill and a valuable tool to build a sustainable energy infrastructure. Yet it faces enormous economic, technical and social challenges. While national governments entertain the concept of 'zero waste' to counter climate change and slow worldwide resource depletion, the public recoils at the arcane science that WtE can represent.

In its most basic form, WtE takes municipal solid waste and transfers it into combustion chambers where it is reduced to ten per cent of its original volume. This process is used to heat water circulating in steel tubes forming the walls, the water subsequently turning to steam and driving turbines to generate electricity.

In the USA over the past 25 years, the WtE industry has developed state-of-the-art technology making it one of the cleanest forms of energy generation. Under the Energy Policy Act of 2005, the Department of Energy (DOE) and 25 states have classified it as a renewable technology, and the DOE maintains that turning waste into energy makes an important contribution to the country’s efforts to achieve increased renewable energy use. Moreover, it says, WtE has many associated positive environmental benefits and meets or exceeds the strictest federal standards set by the US Environmental Protection Agency (EPA).

The 16 MW Pirmasens CHP plant processes up to 180 000 tonnes of commercial/household waste a year Source: Sotec

Yet such a resounding endorsement is lacking elsewhere, particularly in Europe where, on a national basis, the adoption of WtE has been patchy, to say the least. The UK, for example, is sitting on a waste time bomb, with the need to recycle more and bury less in landfill uppermost in recent legislation, yet lags behind Denmark, where burning waste, and so significantly reducing landfill, is an accepted alternative.

More than half of Britain’s rubbish – almost 20 million tonnes a year – goes to landfill, producing vast amounts of methane. By 2020, the UK aims to more than halve the amount of rubbish it buries, to just a quarter of its total waste disposal, but incineration remains unpopular.

As an indication of just how unpopular, you need go no further than the sleepy village of Capel in Surrey, a picture postcard settlement of beamed houses, cricket and woodland, where opponents have fought an eight-year battle to have plans for an incinerator thrown out. The group opposed the plans not on aesthetic grounds, but on what they see as unacceptable emissions from the plant’s chimney. They expressed fears about possible particulate emissions and dioxins, a class of chemical contaminants that are formed during some combustion and industrial processes. Advocates of incineration claim their critics’ fears are unfounded because modern plants are able to operate at temperatures which remove harmful particulates.

 

EU Waste Incineration Directive

 

Still classified as incineration in the European Union (EU)’s Waste Incineration Directive, pyrolysis, gasification and plasma technologies are nonetheless considered more acceptable to the public. They are thermal processes that use high temperatures to break down waste, but use less oxygen than traditional mass-burn incineration. However, they must meet all the mandatory emissions limits that the Directive sets.

Otherwise known as ‘advanced thermal technologies’ or ‘alternative conversion technologies’, pyrolysis, gasification and plasma treatment typically rely on carbon-based waste such as paper, petroleum-based wastes like plastics, and organic materials such as food scraps.

They work by breaking the waste down to create gas, solid and liquid residues, the gases subsequently being combusted in a secondary process. Pyrolysis thermally degrades waste in the absence of air (and oxygen). In the gasification process, materials are exposed to some oxygen, but not enough to allow combustion to occur, usually at a temperature exceeding 750 °C. Pyrolysis can be followed by a second gasification stage in some systems, allowing more of the energy-carrying gases to be liberated from the waste.

Gasification and pyrolysis result in the production of syngas, some 85 per cent of which is carbon monoxide and hydrogen, the remainder consists of carbon dioxide (CO2), nitrogen, methane and a number of other hydrocarbon gases. Because it has a calorific value, syngas may be used as a fuel to generate electricity or raise steam; similarly, it may be used as a basic chemical feedstock in the petrochemical and refining industries, its ultimate calorific value depending on the composition of the input waste to the gasifier.

Gasification and pyrolysis typically conform to a four-stage process, the first involving some form of feedstock preparation in a mechanical biological treatment plant or autoclave. The waste is then heated in a low-oxygen atmosphere to produce a gas, oils and a solid residue, ash. After scrubbing to remove some of the particulates, hydrocarbons and soluble matter, the gas can be used to generate electricity and, in some cases, heat, through combined heat and power (CHP).

Plasma technologies use a plasma arc to heat the waste to a temperature of between 6000-10 000 °C, creating gases and vitrified slag, and may sometimes be used after gasification itself.

These advanced thermal processes are often claimed to have significant advantages over traditional mass-burn incineration. For example, using less oxygen can result in lower air emissions, although in some systems the subsequent combustion of gases and oils arising from the process can generate additional emissions of their own.

Modular in concept and quicker to build than mass-burn incinerators, they offer much more flexibility as they can be added or removed as waste streams or volumes change, for example with increased recycling.

Critics of these advanced thermal processes point out, however, that they may undermine recycling and composting incentives unless they are used solely to deal with only the residual waste. They also rely on the presence of materials such as plastic, paper and food waste to operate efficiently, a prerequisite that conflicts with recycling and composting because these materials are often the most valuable parts of the waste stream.

In a recent report, Juniper Consultancy Services, a specialist in the waste, environmental and bio-energy sectors, explained that while most processes use combinations of these technologies, nearly all of the systems commercially available follow gasification with combustion. ‘In doing so many of the key theoretical differences between pyrolysis, gasification and incineration become blurred,’ it said. ‘While gasification is not the same as incineration, the actual practical differences between some commercial gasification systems – that incorporate combustion to produce electricity – with incineration are relatively modest. Similarly, if pyrolysis is followed by combustion, there is relatively little difference from incineration.’

The 11.6 MW Neunkirchen waste burning power station in Germany began operation in 2001 Source: Sotec

Nor do the technologies involved escape the climate change trap. As they all release fossil fuel derived CO2 from plastics, synthetic textiles and other substances in the feedstock, as well as CO2 from biological materials, critics say energy from such plants cannot accurately qualify as ‘renewable’.

However, a study by Eunomia Research and Consulting concluded that maximizing the removal and recycling of materials, particularly of plastics, avoids emissions from virgin manufacturing processes and so significantly reduces climate impacts. It said it may not be possible to maximize recycling prior to treatment by gasification and pyrolysis because of the requirement for a fairly specific composition of waste, including combustibles, in order for the process to work effectively.

 

Hydrogen Fuel Cells

 

The Eunomia study also observed that syngas can be used in either a gas engine or a hydrogen fuel cell to generate electricity. It said hydrogen fuel cell technologies, in which the syngas is converted to hydrogen, performed somewhat better than CHP in terms of their greenhouse gas impact, largely as a result of greater conversion efficiencies of fuel cells when compared to other energy generation technologies. Yet the study acknowledged that to date very little research has been carried out on the use of syngas derived from municipal solid waste in such applications.

The relative human toxicity of mass-burn incineration and advanced thermal processes is also a key issue driving WtE technologies. Just like incineration, pyrolysis and gasification are likely to produce emissions including acid gases, dioxins and furans, oxides of nitrogen, sulphur dioxide, particulates, cadmium, mercury, lead and hydrogen sulphide. Solid residues include inert mineral ash, inorganic compounds and any remaining unreformed carbon. The quantity and nature of emissions will be different depending on the technology employed, and Juniper’s report says that, in general, pyrolysis and gasification score rather better than incineration in this regard, although, it says ‘the project specific nature of process implementation means that it is inappropriate to generalize.’

The report goes on to talk about the ‘technology risks’ represented by pyrolysis and gasification processes targeting municipal solid waste which, it says, ‘can be significant’. The report continues: ‘One reason for this is that processes…[including those featuring] close-coupled, gasification to gas engines and plasma gasification [technologies], have limited relevant track records. This means that the robustness of guarantees given on factors that may include process availability, maintenance costs and energy output, all of which are necessary to underpin financial models and contract terms, are often called into question in technical due diligence’.

Yet the pursuit of zero waste is destined to ensure that WtE technologies remain firmly on the global agenda. And one company ensuring they do is US firm Covanta, which quotes the EPA as stating that waste-to-energy plants offer a ‘clean, reliable, renewable source of energy, producing electricity with less environmental impact than almost any other source of electricity’.

What is more, WtE means less dependence on imported fuels, reduced greenhouse gas (GHG) emissions and overall represents a safe and effective waste management solution, with less going to landfill.

In December, Covanta began construction on a new energy-from-waste facility in Dublin, Ireland. The project is being built as a public-private partnership between Dublin City Council and Dublin Waste to Energy, which is majority owned by Covanta. The €350 million ($500 million) plant will be able to process up to 600 000 tonnes of waste per year. It is exactly the kind of project that Anthony Orlando, Covanta’s president and CEO, believes can help local authorities in their bid to reduce landfill waste.

“The new energy-from-waste facility will handle post-recycled waste to complement Dublin’s recycling efforts and provide a key component of an environmentally and economically sustainable waste management programme.” he said. “Furthermore, the facility will serve as a new source of clean, renewable energy. This significant investment will deliver long-term value for both the residents of Dublin and our shareholders.”

Covanta will operate and maintain the project, which has a 25-year tip fee arrangement with four Dublin local authorities to provide disposal services for a minimum of 320 000 tonnes of waste annually, representing over half of the facility’s capacity. The remaining capacity will be contracted from the market place, as communities across Ireland reduce their dependence on landfills as required by the EU Landfill Directive which is designed to reduce harmful GHG emissions from landfills. When completed, the plant will generate enough power for 50 000 homes along with district heating potential for 60 000 homes.

That same month, its subsidiary, Covanta Honolulu Resource Recovery Venture, announced a $302 million expansion of the H-Power energy-from-waste facility in Honolulu. The 900 tonnes per day expansion project, which is to be funded and owned by the City and County of Honolulu, will increase the facility’s capacity by 40 per cent. The facility serves as an integral component of the comprehensive solid waste management programme of the City and County of Honolulu.

The moves are indicative of the pace of development, worldwide, of WtE and globalization, which last month saw Covanta take further steps to extend its position in overseas markets. In December, the company emerged as the latest suitor in the contest to take over UK waste management group Shanks. The $2.6 billion quoted firm entered the UK market four years ago and is using its British foothold as a base from which to expand in Europe.

The UK currently lags far behind most of its European counterparts when it comes to waste management and recycling, and is looking at ways to cut the amount of waste – currently 56 per cent – going to landfill. Although the recycling rates have increased dramatically over the last few years, landfills are reaching capacity at a rapid rate. This has led to the energy-from-waste business becoming one of the fastest growing segments of the waste management industry.

An £80 million ($128 million) WtE plant is to be built at the site of the Ford Motor company’s former manufacturing facility at Dagenham, Essex, UK, and plans were approved last month for another energy-from-waste incinerator in Exeter in the south west of the country. The latter, a 60 000 tonne facility will be designed, built and initially operated by Viridor Waste Management, burning non-hazardous waste to generate electricity.

WtE plants have stirred up considerable opposition from some green groups in the UK, where more than 100 waste incinerators are currently being planned. Critics of the technology claim that because up to a third of the waste burned is derived from fossil fuels, the plants are still relatively carbon intensive when compared with other forms of renewables.

But as WtE is increasingly coming to be recognized as an approach capable of resolving two major issue in one – waste management and sustainable energy, Britain’s government is encouraging the technologies. It has made biomass facilities – including WtE plants – a key component of its recently published renewables strategy. WtE could be contributing up to six per cent of the UK’s electricity by 2020.

Worldwide, during the 2001-2007 period, it has been estimated by the International Energy Agency that the WtE capacity increased by around four million tonnes per annum. Japan and China built several plants that were based on direct smelting or on fluid bed combustion of solid waste.

In China, there are about 50 WtE plants. Japan is the largest user in thermal treatment of municipal solid waste in the world with 40 million tonnes and Denmark has 29 energy-from-waste plants, which treat 26 per cent of the total amount of waste the country generates, producing environmentally friendly electricity and district heating. Heat from WtE facilities is generally the cheapest source of heating in Denmark.

The simple fact is that waste is too valuable to waste, representing as it does an increasingly important fuel source. WtE’s advocates maintain that using waste as a fuel source can have important environmental benefits, providing a safe and cost-effective way of waste disposal while helping to reduce CO2 emissions.

 

More Powe Engineering International Issue Articles

 

 

Powe Engineering International Archives

 

 

View Power Generation Articles on PennEnergy.com