Energising Waste

Using waste to generate energy, be that as heat or electricity, appears a natural solution to two problems and a logical part of industry’s transition to greater circular thinking. Making use of what has already been collected instead of letting it rot as landfill not only makes environmental sense, but it’s also economically viable, which is why it is attracting so much ethical investment. WtE, as it is known, usually involves processes that generate power directly through combustion, or produce a combustible fuel commodity, such as methane, methanol, ethanol or synthetic fuels, which means modern incineration plants have to be capable of meeting strict emission standards, especially those that involve nitrogen dioxides and dioxins rather than those designed to merely burn to reduce volume.

There are also many other emerging technologies that can do the same with the use of direct combustion. Many of them are believed to be able to produce more power from the same amount of fuel, mainly because of the separation of corrosive components from the converted fuel which allows for higher combustion temperatures. Not surprisingly, there is no shortage of projects to accelerate the pace of innovation here; such as one undertaken by engineers at the University of West Virginia into recycling single-use plastic packaging by upcycling them into petrochemicals.

Yuxin Wang, a research assistant professor and principal investigator of the project, explained: “Americans throw away 100 billion plastic bags annually, that’s about 307 bags per person. Singleuse plastic waste ends up in landfills or the water, harming the ecosystem and natural environment. Most of the energy and carbon in plastic wastes will be recovered and the proposed technology will reduce carbon dioxide emissions significantly.”

Since the 1950s, the rate of plastic production has grown faster than any other material, with only nine per cent of plastic waste ever produced having been recycled, according to a report by the United Nations Environment Programme.

Wang insists that current technologies to upcycle single-use plastics are energy intensive, causing a high volume of greenhouse gas emissions and prohibiting large-scale upcycling. To tackle this, researchers from the Statler College of Engineering and Mineral Resources identified a one-step microwave catalytic process to upcycle them into high value benzene, toluene and xylene for use as petrochemicals. Wang explained that this will enable cross-industry reuse of recycled feedstock and reduce primary fossil fuel consumption.

Wang said: “The produced ethylene and BTX aromatics from plastic upcycling can be used as feedstocks to re-make plastics. That will reduce demand on fossil fuel derived ethylene and BTX aromatics from conventional petroleum refinery, leading to a reduction in greenhouse gas emissions.”

Opponents have expressed concern that by encouraging energy from waste, recycling will be discouraged, something that has prompted ministers in the UK Government to move waste up the hierarchy of priorities, following examples elsewhere in Europe where energy from waste coexists with high recycling, ultimately resulting in low landfill. There are also concerns that WtE may compete with, not complement, recycling, which means plants and processes have to be flexible enough to adapt to changes in waste arisings and composition. Waste infrastructure has a long lifetime and care needs to be taken at the start to ensure systems can adapt to potential long-term change and drive waste up the hierarchy, not constrain it.

Advocates argue that waste doesn’t have to be just about waste management. The energy it produces is a valuable domestic source contributing to energy security. It has the added advantage that it is non-intermittent, so it can complement other renewable energy sources such as wind or solar.

The majority of most of the WtE output becomes electricity. But increasingly plants are also looking to use the heat it generates and, longer term, there’s potential to transform it into other energy sources such as transport fuels or substitute natural gas.

According to the latest data from the Estonian WtE specialists Waste to Energy International, there are more than 2,500 waste-to-energy plants in the world, including almost 500 in Europe. The type of wastes generally burned in them include municipal solid waste (MSW), human sludge, hazardous industrial, medical and biological waste.

Having completed a project with French company ATI Industries to build a Russian plant designed to process 24,000 tons of medical and biological waste annually, they say the technology needed differs from that used in MSW plants.

“Processing hazardous medical and biological waste requires significantly higher temperatures in the furnace to destroy malignant bacteria and viruses,” according to their published views online. They go on to add: “Rotary kiln technology provides a higher temperature up to 1,100 °C with longer exposition. To compare, incinerator on reciprocating grate processes municipal solid waste at 850 °C with an exposition of two seconds.”

The major by-product of a waste to energy plant is the ash. The incineration plant produces two types: bottom ash from the furnace and so-called fly ash, from gas cleaning system filters. Whilst bottom ash can be used in the construction of roads or the production of bricks, the fly ash is hazardous and must be buried in landfills. Fortunately, that comprises only two-three per cent of the initial waste tonnage. Bottom ash output usually equals 10-15 per cent.

In Italy, IBT Connecting Energies GmbH have secured orders for two waste-toenergy projects in the Sardinia region. Three C65 microturbines will be deployed at two wastewater treatment facilities operated by Acciona Agua SA in Alghero and Cagliari, Italy. The microturbine systems are expected to be commissioned in December. It's a similar pattern elsewehere in the world.

In Australia, the refuse giant, Cleanaway, is to build two waste-to-energy plants at a cost of up to $2 billion in Victoria and Queensland, having acquired an 82-hectare farm at Wollert and a 50-hectare site outside Brisbane.

In United Arab Emirates, Emerati company Masdar has opened a new WtE facility in Sharjah, the first of its kind in the Middle East and the work of Emirates Waste to Energy, a joint venture between Masdar and Bee'ah — another sustainability focused firm in the Emirates.

In Kenya, plans have been announced to host an inaugural two day Waste-to-Energy Congress aimed at tackling the worsening waste management challenges facing the country. It was organised by Hitachi Zosen Inova (HZI), of Zurich in partnership with Sintmond Group, a local Smart Waste project management firm.

In Dubai, an official Municipality announcement said that it has begun the installation of a steam turbine at the Dubai Waste Management Centre, the world’s largest waste-to-energy project located in the Warsan area.