Feature article

72 renewable energy focus May/June 200872 renewable energy focus May/June 2008

Tapping into the power of energy from wasteOLD PARADIGMS ARE BEING TRANSFORMED AND RESHAPED AS

ALTERNATIVE, SUSTAINABLE SOLUTIONS ARE SOUGHT TO MEET THE

WORLD’S GROWING ENERGY NEEDS. THIS CHALLENGE IS BEING FUELLED

IN PART BY THE EXPANDING ECONOMIES OF BOTH CHINA AND INDIA,

COUPLED WITH ISSUES OF GLOBAL WARMING, ENERGY SECURITY,

AND DEPLETING RESOURCES OF FOSSIL FUELS. ONE LEADING ENERGY

FROM WASTE EFW PLAYER, COVANTA, LOOKS TO WHAT EXTENT EFW

TECHNOLOGY COULD REALLY PLAY A ROLE. Derek Porter

Covanta Bristol, an Energy-from-Waste facility in Bristol, Connecticut, USA.

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renewable energy focus May/June 2008 73

Energy from waste

renewable energy focus May/June 2008 73

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 EfW 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,

EfW is increasingly gaining attention as a solid waste disposal method

that can generate clean, renewable energy.

Benefi ts of EfW

The EfW process addresses both the need for clean, renewable energy,

while reducing the need to landfi ll solid waste, and reducing greenhouse

gas emissions caused by landfi lling 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 renew-

able energy.

But unlike coal, oil, or natural gas, there is an abundant supply of household

garbage left after rigorous recycling eff orts, 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, EfW 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 landfi lls, it gives off a large variety of

off -gases. One of the principle gases emitted by landfi lls is methane.

Twenty-one times more potent than CO2, methane from landfi lls contrib-

utes signifi cantly 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 Envi-

ronmental 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, landfi lls can only recover

about 20% of the energy that can be captured with EfW. Unlike landfi lls,

however, for each tonne of waste combusted in an EfW facility, there is an

accompanying reduction of approximately one tonne of CO2 equivalent

greenhouse gas emissions.

Today, EfW processes handle approximately 140 million tonnes of MSW

around the world. This translates into a corresponding reduction in green-

house gases in the vicinity of 140 million tonnes per year.

Global perspective

As noted by Patrick Moore, Greenpeace co-founder and chairman of

Greenspirit Strategies Ltd. in Vancouver, “a fl exible 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, http://www.thestar.com/article/185200].

Around the world, more communities have begun to embrace this tech-

nology and tap into the power of EfW. 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, EfW has been

adopted as the preferred method of waste disposal in a wide-range of coun-

tries, 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, http://www.waste-management-

world.com/articles/article_display.cfm?ARTICLE_ID=304395&p=123].

With nearly 400 facilities located across Europe, the increased use and

interest in EfW signals a dramatic shift away from landfi lls. According to

Grapple lifting Municipal Solid Waste (MSW) at a Covanta Energy Energy-from-Waste facility.

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Energy from waste

74 renewable energy focus May/June 2008

Frost & Sullivan, EfW 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, http://www.waste-management-world.com/

display_article/318353/123/ARTCL/none/WTENE/1/The-European-WTE-

market-is-buzzing/].

Driving this growth is an EU directive requiring a 65% reduction in the

landfi lling of biodegradable MSW by 2016, which has tipped the scales in

favour of EfW as the preferred waste disposal alternative. In addition, EU

countries have focused on using EfW as a method to specifi cally 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 EfW process, these regions use the heat generated during combustion

for district and industrial heating purposes.

And in Asia, EfW has been strongly embraced in Japan, Korea, Singapore,

and China. For example, Japan – faced with preserving open space or

using landfi lls – 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 EfW facilities.

Similarly, China’s growing economy has led to an increased need for renew-

able 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 EfW to process its MSW to 50% by 2030.

In north America, US environmental regulators today recognise the dual

contributions of EfW. 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 fi nally, landfi lling. The

US EPA recognises EfW as a renewable energy, and has declared that EfW

generates power with “less environmental impact than almost any other

source of electricity” (see Joint letter from the Assistant Administrator, Offi ce

of Solid Waste and Emergency Response, USEPA and the Assistant Adminis-

trator, Offi ce of Air and Radiation, USEPA to the president of the Integrated

Waste Services Association – IWSA – dated 2/14/03). Today, there are 89 EfW

facilities in the USA converting approximately 29 million tonnes of waste

per year, into more than 17 million MW hours of energy.

Globally, EfW is proving to be an eff ective 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 EfW opponents have raised is that the process reduces recy-

cling rates. However, the EU’s Environment Agency report on Europe’s Envi-

ronment recently noted that there was no evidence that those allegations

were true.

Indeed, countries like Denmark, Sweden and Germany, who rigorously

embrace EfW, have experienced a corresponding improvement in recycling

rates. In the US, municipalities with EfW plants have also seen their recycling

eff orts improve.

The future

Our world is changing rapidly and it is imperative that we develop scaleable,

practical solutions for our energy generation needs, which reduce the

damaging eff ects of climate change, and limit the release of dangerous

greenhouse gases. In that climate, EfW has emerged as a leading option for

renewable energy generation and sustainable waste management. The ability

of EfW facilities to both off set 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, EfW is one tech-

nology that has been tried, tested and embraced, and which can be

expanded further to address our growing energy needs.

Advances in EfW – NOx reduction

Even with all of the advances that the EfW industry has made in the past 20 years with regard to emissions reductions, addressing nitrogen oxide (NOx) emissions generated during the EfW process remains an important objective for the industry. Among the inno-vations making today’s EfW facilities more energy effi cient and environmentally sound are eff orts 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, EfW 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 EfW 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 effi ciency of the process. As the tech-nology is still evolving, it is possible that additional innovations could further reduce NOx emissions to even lower levels in the future.

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About the author:Derek Porter serves as vice president of external aff airs for Covanta Energy Corp. He is responsible for a variety of duties, including managing internal and external communications, public aff airs and community relations.

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