Planning Implications for Increased Use of Waste-to-Energy Technologies
Waste management is changing. In the past, the focus was on disposal, but now in many countries, there is a growing recognition that waste should be viewed as a “resource opportunity.” This shift in perception is prompted by incentives to protect the environment, movements to encourage renewable energy generation, a decrease in landfill availability and a greater focus on resource efficiency.
“In terms of strategy and execution, the approach by many countries toward waste management has, historically, remained siloed,” said Andy Powell, Black & Veatch’s Technical Director, Water EMEIA (Europe, Middle East, India & Africa). “This is gradually changing, with increased integration across industry, infrastructure, utilities and municipalities, in the way waste is managed.”
In the UK and elsewhere, the market is evolving rapidly. “Growing competition for waste as a feedstock means front-end economic value is being surpassed by the value that can be created in the processing and re-use phases,” Powell said. The back end of the waste management value chain is becoming increasingly significant as a result of the ability to create:
- High-quality digestate for use as a soil enhancer/fertiliser;
- High-quality compost;
- Heat export to replace gas heating of the built environment;
- Electricity export to displace electric grid imports;
- By-products such as construction industry aggregates;
- Biogas upgrade to gas-to-grid, as well as vehicle transportation fuels;
In addition, waste to energy is considered a “schedulable” renewable energy, which helps balance the intermittency of most other renewables.
Integrated and Holistic Planning
This increase in value is having a significant impact upon planning. Previously, waste management planning focused on the transportation from the source to the disposal site. According to Powell, “As back-end conversion products begin to drive the economics of waste management, approaches to planning need to become more integrated and holistic, and take into account the total cycle resource utilisation.”
Anaerobic digestion (AD), the decomposition of organic feedstocks by micro-organisms in the absence of oxygen, is a well-established method of dealing with organic waste, both liquid and solid. The process generates biogas that can be utilised as a source of renewable energy. AD has been used at sewage treatment facilities for more than 100 years.
AD provides a way of extracting the best value – both calorific value and by-product utilisation – when the organic fraction is broken out. For example, the front-end segregation of the feedstock into constituent elements will optimise resource recovery and conversion. Small-scale AD plants, less than 20 kilo-tonnes per annum (ktpa), do not have the economies of scale, but medium-scale plants make good economic sense as a waste-to-energy source.
Large-scale energy from waste (EfW) combustion technologies, greater than 250 ktpa, are now well established and have good economies of scale. Local reaction to such plants, however, is often negative, Powell noted. Emission issues and concerns from earlier generation plants have long since been addressed, but the legacy remains.
EfW efficiency is around 25 percent due to the steam cycle for electricity generation. However, the electrical efficiency of biogas engines, the type that can be fuelled by AD by-products, is around 37 percent. In countries where district heating networks are uncommon, EfW plants tend not to be located close to large numbers of energy users, so the ability to use waste heat from the process to improve overall efficiency is depleted. In these instances, many EfW facilities are converting waste materials to waste heat, which Powell calls “a major missed opportunity.”
New thermal waste management technologies such as gasification, pyrolysis and gas upgrade have yet to be proven on a large, commercial scale, but they are on the cusp of widespread improvements and subsequent adoption, Powell said. The planning issues associated with these burgeoning technologies include:
- Certainty of flue gas emission quality;
- Safety of high pressure/temperature processes;
- Disposal of resultant ashes and liquors;
- Demand of water for energy production in drought-intolerant areas.
As the resource recovery industry – as Powell prefers to call the waste management sector – matures, innovations and asset management techniques will be developed to better maximise efficiency and business performance. One such development is the autoclaving of mixed waste, which allows the separation of organic materials from other recyclables.
“Technology is only part of the equation. True application of resource efficiency can only come from education and awareness and, eventually, greater public buy-in,” Powell said. “As this happens, what we currently view as waste will increasingly be perceived as a valuable resource and fuel.”
Story by Malcolm Hallsworth, Black & Veatch