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Cost of Combustion

July 22, 2008

By SHILLINGTON, David

Combustion has become widely-researched and highly-effective process, but what is it doing to the environment? —————— — Combustion processes (including wood burning) have been extensively researched, particularly since the advent of the internal combustion engine and the development of the aerospace industry. As a result motor cars of today are far more fuel efficient.

The term combustion is used to describe the process whereby a fuel source is oxidised by oxygen or other oxidising material (for example nitrous oxide for extra energy in motor racing).

When combustion is fast enough, sufficient heat can be produced to cause fire and flames.

In the case of a very slow oxidation, such as in the special case involving iron (rusting) the cost to society is enormous through replacement of deteriorating equipment.

In humans and animals, respiration (through breathing) occurs via a complex series of enzymatic (catalytically) controlled processes, which enable us to add oxygen to the food we eat at the low temperature of 37deg (body temperature).

In addition to releasing energy, we produce carbon dioxide, water and many other toxic waste materials, which have to be excreted to avoid poisoning our bodies. This is typical of many combustion processes, where unwanted waste products are produced.

At the other extreme, an explosion is an extremely fast (runaway) combustion reaction.

In this case, the speed of the oxidation processes increases as the temperature rises, producing an increasing amount of heat.

This in turn raises the temperature, further speeding up the reaction until the explosion is complete.

The whole process depletes the entire fuel source in a fraction of a second with huge energy production, useful for munitions and explosives. The trick in rocket propulsion and fuel oxidation is to burn considerable amounts of fuel without allowing the explosive process to take over.

In the case of burning wood or tobacco, many types of chemical by- products form in the process. The remaining ash (produced when the fire has been efficiently used and very hot) will contain the oxides of metals and minerals originating from the wood.

Some of these include calcium, magnesium, sodium and numerous heavy metal oxides derived from the heavy metals (such as lead and chromium), depending on the composition of the soils at the time of growth.

The uptake of metals by plants formed the basis of groundbreaking studies by the Massey University scientist and late emeritus professor Robert Brookes.

After having worked with moon rock specialist (Professor Ahrens – a geochemist) at the University of Cape Town in South Africa, Prof Brookes put Massey on the world’s scientific map by studying mineral uptake in plants.

Together with Roger Reeves and other scientists, he postulated useful remediation plans to use plants on contaminated soils, and then to harvest them to recover the metals.

Studies by other scientists investigated the presence and concentration of heavy metals found in individual tree rings to quantify historical patterns of uptake during earlier decades of growth.

It has been found that the toxicity of organically-bound lead obtained from plant material is more toxic than simple lead salts of similar concentrations, when lead salts are dissolved in water.

Combustion during the past two centuries has been extremely useful for locomotion, heating, materials manufacture and many other applications.

However, the downside to this use has been the increasing emissions, which continue to rise to unacceptably high levels as the world’s population continues to grow and demand for energy use increases.

With two and half weeks to go before the Olympic Games, we all hope the emissions in Beijing will be cleaned up sufficiently for our athletes to breathe easy.

* David Shillington is head of the School of Applied Health Sciences at UCOL.

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(c) 2008 Evening Standard; Palmerston North, New Zealand. Provided by ProQuest Information and Learning. All rights Reserved.




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