One of the most readily-available and viable solutions to address our growing energy needs is energy-from-waste (EfW). This is a process that takes municipal solid waste (MSW) – such as household rubbish – and converts it into energy. During the energy-from-waste process, waste passes through combustion chambers at high temperatures, reducing it to 10% of its original volume. Steel tubes that form the walls of the combustion chambers are heated, transforming water in the tubes to steam that is sent through a turbine to continuously generate electricity.
Often overlooked when compared with ethanol, wind, and solar power, energy-from-waste is increasingly gaining attention as a solid waste disposal method that can generate clean, renewable energy.
Benefits of energy-from-waste
The energy-from-waste process addresses both the need for clean, renewable energy, while reducing the need to landfill solid waste, and reducing greenhouse gas emissions caused by landfilling of MSW.
Each tonne of solid waste has the energy value of about one barrel of oil or ¼ quarter tonne of coal, enough to produce about 600 kWh of renewable energy.
But unlike coal, oil, or natural gas, there is an abundant supply of household garbage left after rigorous recycling efforts, and this can be tapped into as a fuel source. Energy-from-waste can provide a steady current of energy to the grid. Operating 24 hours a day, 7 days a week, energy-from-waste facilities are consistent and reliable in generating renewable energy. And this is an important factor when considering both the growing demand for energy, and the ability to meet the demands of consumers.
As organic matter decomposes in landfills, it gives off a large variety of off-gases. One of the principle gases emitted by landfills is methane. Twenty-one times more potent than CO2, methane from landfills contributes significantly to global warming.
Some landfills address the problem of off-gases by building engines or turbines that can capture the methane for electrical production. In the USA, landfill gas collection is used at some landfills part of the time, but only a fraction of the landfill gas is actually captured. The US Environmental Protection Agency's (EPA) nationwide inventory – and the Earth Engineering Centre at Columbia University – estimate that only about 50% of landfill methane is captured over the life of the landfill (that includes landfills with no methane collection systems). The rest is vented into the atmosphere.
Most landfills do not capture that source of energy during the initial years of its operation, or after closure. This methane escapes directly into the atmosphere, or is combusted with no energy recovery.
In comparison, assuming good capture rates, landfills can only recover about 20% of the energy that can be captured with energy-from-waste. Unlike landfills, however, for each tonne of waste combusted in an energy-from-waste facility, there is an accompanying reduction of approximately one tonne of CO2 equivalent greenhouse gas emissions.
Today, energy-from-waste processes handle approximately 140 million tonnes of MSW around the world. This translates into a corresponding reduction in greenhouse gases in the vicinity of 140 million tonnes per year.
As noted by Patrick Moore, Greenpeace Co-Dounder and Chairman of Greenspirit Strategies Ltd. in Vancouver, “a flexible approach to managing our waste disposal might see the recovery of energy from all carbon-based materials that are unsuitable for recycling.” [see “Waste Not,” The Toronto Star, 26 February 2007].
Around the world, more communities have begun to embrace this technology and tap into the power of energy-from-waste. A review of the industry by the Waste-To-Energy Research and Technology Council (WTERT) has shown that global capacity has increased steadily at the rate of about four million tons of MSW processed per year since the beginning of this century. In fact, waste-to-energy has been adopted as the preferred method of waste disposal in a wide-range of countries, and in more than 778 facilities processing more than 140 million tonnes of waste per year [see article by Nickolas Themelis, Thermal Treatment Review, Waste Management World, July-August 2005, ].
With nearly 400 facilities located across Europe, the increased use and interest in energy-from-waste signals a dramatic shift away from landfills. According to Frost & Sullivan, energy-from-waste capacity is expected to increase by almost 13 million tonnes, with close to 100 new plants coming on line by 2012 [see article, The European WTE Market Is Buzzing, Waste Management World, 28 January 2008].
Driving this growth is an EU directive requiring a 65% reduction in the landfilling of biodegradable MSW by 2016, which has tipped the scales in favour of energy-from-waste as the preferred waste disposal alternative. In addition, EU countries have focused on using energy-from-waste as a method to specifically reduce greenhouse gases and comply with the Kyoto Protocol.
Energy-from-waste is strongly supported in Scandinavian countries for its co-generation capabilities. In addition to using electricity generated from the energy-from-waste process, these regions use the heat generated during combustion for district and industrial heating purposes.
Advances in EfW – NOx reduction
- Even with all of the advances that the energy-from-waste industry has made in the past 20 years with regard to emissions reductions, addressing nitrogen oxide (NOx) emissions generated during the energy-from-waste process remains an important objective for the industry. Among the innovations making today's energy-from-waste facilities more energy efficient and environmentally sound are efforts to improve the traditional combustion processes that can result in lower NOx emissions;
- Traditionally, the industry standard has been to use Selective Non-Catalytic Reduction (SNCR) post-combustion NOx technology, which relies on injecting an ammonia reagent into the process to successfully lower NOx emissions to levels that meet today's existing requirements;
- While SNCR is a viable method to control NOx, it is limited in how much reduction can be achieved, even when increasing the ammonia reagent. As a result, energy-from-waste specialists Covanta has taken a closer look at modifying existing equipment – as well as the combustion process – in ways that enhance the SNCR process and further lower NOx emissions without relying on additional reagent;
- Typically, municipal waste combustors employ a moving grate with two major sources of combustion air; primary and secondary air. Using advanced modelling techniques, Covanta's research and design team found that lower NOx emissions can be achieved by introducing a third major source of combustion air, a tertiary gas system. This tertiary gas stream inhibits NOx formation from the burning waste;
- According to Covanta, the patent pending technology – called VLN – has been demonstrated to enhance the performance of an SNCR system. It reportedly optimises the ammonia injection while also successfully reducing NOx emissions to levels well below any previously achieved by the energy-from-waste industry in the USA;
- Initial pilot projects have demonstrated NOx emissions of more than 50% below that of the US EPA's requirements, as well as having increased the energy efficiency of the process. As the technology is still evolving, it is possible that additional innovations could further reduce NOx emissions to even lower levels in the future.
And in Asia, energy-from-waste has been strongly embraced in Japan, Korea, Singapore, and China. For example, Japan – faced with preserving open space or using landfills – has adopted the technology to deal with the increasing volume of MSW generated by the growth of its economy. Today, 70% of Japan's MSW is processed at energy-from-waste facilities.
Similarly, China's growing economy has led to an increased need for renewable power, generation, and sanitary waste disposal. Unlike Japan, however, the country has only recently embraced this technology and has issued a directive to increase usage of energy-from-waste to process its MSW to 50% by 2030.
In north America, US environmental regulators today recognise the dual contributions of energy-from-waste . As it is throughout the developed world, solid waste management in the USA is based on a hierarchy that recommends reduce, recycle / compost, combust with heat recovery and finally, landfilling.
The US EPA recognises energy-from-waste as a renewable energy, and has declared that energy-from-waste generates power with “less environmental impact than almost any other source of electricity” (see Joint letter from the Assistant Administrator, Office of Solid Waste and Emergency Response, USEPA and the Assistant Administrator, Office of Air and Radiation, USEPA to the president of the Integrated Waste Services Association – IWSA – dated 2/14/03). Today, there are 89 energy-from-waste facilities in the USA converting approximately 29 million tonnes of waste per year, into more than 17 TW hours of energy.
Globally, energy-from-waste is proving to be an effective technology capable of harvesting an abundant fuel source to generate clean, renewable energy. But like many other renewable energy sources it is not without its detractors. One of the biggest concerns energy-from-waste opponents have raised is that the process reduces recycling rates. However, the EU's Environment Agency report on Europe's Environment recently noted that there was no evidence that those allegations were true.
Indeed, countries like Denmark, Sweden and Germany, who rigorously embrace energy-from-waste , have experienced a corresponding improvement in recycling rates. In the US, municipalities with energy-from-waste plants have also seen their recycling efforts improve.
Our world is changing rapidly and it is imperative that we develop scaleable, practical solutions for our energy generation needs, which reduce the damaging effects of climate change, and limit the release of dangerous greenhouse gases. In that climate, energy-from-waste has emerged as a leading option for renewable energy generation and sustainable waste management. The ability of energy-from-waste facilities to both offset dangerous greenhouse gases and to provide reliable sources of renewable energy have emerged as great advantages.
Reaching our energy goals will require international cooperation and the sharing of ideas and best practices across national lines. We are all being asked to address what appears to be an unquenchable thirst for energy. Shifting the global community away from fossil fuel and towards more sustainable energy practices will require close evaluation of every available option.
While there is no single answer to our energy challenges, energy-from-waste is one technology that has been tried, tested and embraced, and which can be expanded further to address our growing energy needs.
About the author
Derek Porter serves as Vice President of External Affairs for Covanta Energy Corp. He is responsible for a variety of duties, including managing internal and external communications, public affairs and community relations.