Monthly Archives: October 2011

Is The Waste Really Worth It?

This blog is also about generating energy from a source that is available in plenty/excess all over the world. A question might arise as to why an engineer from the lighting design group is writing about energy generation. Energy is in short supply all over the world, and its requirements are increasing by the hour. Recently while watching a BBC program on generating energy from waste, I found it captivating and I thought that should share some details with my colleagues and our community.

Denmark has long relied on waste to energy process for dealing with municipal waste. Its first plant was commissioned in 1903 and from the start this method of waste disposal was linked to supplying heat for district heating system and energy for power generation Copenhagen (capital of Denmark) processes 25-40% of its waste this way, three quarters of its household refuse, producing some 720,000MW of heat and 210,000MW of power. Statistics for the year 2008 is given below.
Waste received–1500-1600 Tonnes daily
Waste Breakdown–50% Domestic
Waste Incinerated–563000 Tonnes
Bottom ash produced—100,000 Tonnes
Flue gas waste produced–300,000 Tonnes
Households supplied with heat and power–1,55,000 District heating energy–1390 GW (1GW=1000MW) Electricity–2450 GW.

Municipal waste is delivered by road and tipped into huge concrete bunkers. It is mixed and extracted by crane grabs and fed into shafts leading to the furnaces. Here the waste sits on moving grates that take it through the flame. Hot exhaust gases leave the furnace and heat the water in a series of heat exchangers The hot water, or steam, can be used directly for district heating, or the steam used to drive turbines to produce electricity.

The incineration of waste results in ash or slag at the bottom of combustion chamber, and fine particles (Fly Ash) in the exhaust gases.
These gases often contain hazardous substances and must be treated, or scrubbed as well as filtered before discharging through the chimney stack. The bottom ash can be cleaned and recycled as concrete additive–bottom ash residues amount to about 200Kg. per tonne of waste. Fly ash may be disposed as hazardous waste in accordance with environmental standards. This process is also widely used in Japan and Korea. Since the byproducts and residues could be hazardous, some countries are resistant to this process. There are other technologies like gasification, depolymerisation and pyrolysis. Non thermal technologies include anaerobic digestion, fermentation and mechanical biological treatment. In addition to incinerating 39% of the collected material for energy, Copenhagen also recycles 56% of them. The improvement in Copenhagen’s recycling system has reduced its carbon dioxide emissions by 40,000 tonnes since the systems implementation.

Architecturally, the latest waste treatment plant has a sloping SKI slope (31,000 sq. mtr) on its roof. The slope is ecological using a recycled synthetic granulator, upending the convention of the energy intensive indoor ski resort. The smoke rings coming out of the smoke stack is in the form of rings 30M in diameter At night heat tracking lights are used to position lasers on the smoke rings into glowing artworks.

What is in it for us? Every village to big city generates so much of waste every day. They are just deposited outside the city limit. They have already become big mountains. After the rains they are big source for communicable disease. We must do something NOW. If venture capitalists are willing to fund it, small entrepreneurs must come forward and set up plants in every big city to start with. The savings are enormous. The govt. should also wake up and provide subsidies to these kinds of projects.

Written by: R. Sitaraman