Design - DSGN 215 - Engineering and the Environment

Introduction

This is an area of increasing concern as it is more widely realised that the planet Earth does not provide an infinite capacity for absorbing waste materials. This has led away from previously accepted practices that if the pollutant was sufficiently diluted or dumped in a sufficiently remote / inaccessible place, then this was ok. Global warming and growing gaps in the ozone layer are indications that wastes have far reaching effects that can not at present be predicted with any confidence. To provide data about pollution, some countries have set up networks of sampling points to monitor both atmospheric and water born pollution. It is essential that engineers have some understanding of environmental issues so that they will be able to design products and systems that will be acceptable in the 21st century.

Key areas where environmental matters need to be considered are listed below:

Extracting and refining raw materials. Manufacturing products and chemicals. Use of products, materials. Disposal / reconditioning of products at the ends of their useful lives.

Extraction of Materials

Extraction of raw materials can leave the landscape in an unsightly condition. Even as long ago as the 1860s the Duke of Bedford issued leases for mining at Devon Great Consols on condition that the land was restored to the original condition when the mining was complete. It is now very common in many countries for regulatory authorities to insist on this. The transport infrastructure required to move extracted materials may also be contentious.

A major hazard that frequently needs to be guarded against is pollution of water courses by material that is washed off site by routine rain or by flood. As these phenomena depend upon the weather, there is a degree of statistical uncertainty in carrying out assessments of the possible scale of the potential problem or damage. Mathematical modelling is increasingly applied to studies of possible pollution spread, however, as with all modelling, the accuracy of the answers depends upon the accuracy of the input data - and water flow in excess of that modelled (or some other misjudgement) may well render the results worthless.

A series of shallow, but large surface area, settling tanks are frequently provided to assist solid matter in dropping out of suspension. More complete removal of solid matter will require filter beds or centrifuges.

One potential source of many materials which would involve minimum environmental damage if processed, is sea water, but this has not really attracted any serious commercial applications. It is however believed that some areas of the Pacific seabed have valuable nickel rich nodules. These however are in deep water and recovery would be expensive.

Refining / Processing of Materials

In many cases this involves heating. As fuel costs rise, it is increasingly important to make efficient use of energy, by recovering waste heat to provide steam for electrical generation or heating. Many processes require small particle sizes, which necessitates grinding up material, this causes dust which may need to be controlled and - for high value products - recovered.

Manufacturing

ICI in Cheshire developed products that could be made from salt (sodium chloride). The company grew by considering what waste product was left when they had made their main product, then considering how they could best turn this 'waste' into some other chemical that could be sold. This process inturn gave rise to unwanted 'waste' which was turned into yet another saleable product. ICI Mond Division consequently developed many products with comparatively few 'wastes' (chemicals that could not be sold). Many low cost materials that are fairly inert and have no obvious uses (potential wastes) may be usable as fillers for plastics, as a constituent in building / insulation blocks, or in road construction.

In engineering manufacturing emphasis is now placed on producing items with a minimum of waste, by using 'near net shape' processes such as casting or forging wherever possible and by minimising the use of machining. Even though swarf can be recycled, this is not very efficient and waste cutting fluids need to have the solids extracted before thay can be recovered and recycled. The cost of the system to remove the solids from the fluid in an electrical discharge machine is likely to be a significant portion of the total machine cost. Centrifuging and filtering are commonly used.

Many cleaning processes are used during manufacturing and these are subject to restrictions to prevent organic vapours escaping into the atmosphere and to prevent contaminated liquids entering the drains. Degreasing plants using organic solvents are now often totally enclosed and there are restrictions on what solvents are permitted. Where water based cleaning is used, it is necessary to separate any oil from the water before disposal. Because of the need to remove virtually all wastes from water before it can be disposed of, an increasing number of companies are re-cycling their water, with little going to waste and only occasional top up being needed.

Because consumers are demanding products with longer lives, products must be better able to resist gradual deterioration due to wear and environmental attack. Designers need to have a good understanding of materials engineering, including tribology, if the products they design are to have long lives with a high reliability.

Use of Products.

In the middle of the 20th century, coal was the main source of energy in the UK and atmospheric pollution in and around large connurbations, resulting in 'smog', was a was a serious health hazard. Oil, which causes less pollution than coal, gained ground as an energy source until an energy crisis in the 1970s caused a rapid increase in it's price. Natural gas, which causes less pollution than oil, has recently increased it's share of the energy market. However burning any of these fuels releases the greenhouse gas, carbon dioxide. To provide energy without the production of carbon dioxide requires the burning of hydrogen, or the use of nuclear energy, fuel cells, solar, wind or wave power. Nuclear energy is unpopular with many people because of concerns about safety and waste products, especially in the long term. The 'renewable' energy sources are still able to provide only a small portion of the UK energy requirements.

Mechanical Engineers are concerned with things that move. To save energy, they need to be as light as possible. Generally to increase productivity they should operate quickly, hence friction should be kept as low as possible by choice of appropriate bearings, to prevent wasted energy appearing as unwanted heat.

Most major car companies are taking steps to lighten their vehicles while improving their quality, to improve the efficiency of existing types of engine while reducing their unwanted exhaust emissions and investigating new power systems. Modern lubricants for automobile engines are formulated to give low exhaust emissions while causing a minimum energy loss.

Blaming all atmospheric pollution on cars is however a simplification, as waste energy caused by heat losses from buildings is thought to cause even more pollution. Aircraft also generate more atmospheric pollution per person km than road vehicles.

Disposal of Products.

As many industrialised countries are running out of landfill areas, where domestic and non-hazardous waste can be dumped, there is increasing pressure to reduce the volume of a such waste. This is being tackled in several ways. Simple economics is forcing up the cost of landfill, particularly at those sites near to centres of population. Governments in some countries are adding extra pressure by imposing landfill taxes. In Europe manufacturers of cars are responsible for ensuring that there are facilities in place for taking back the cars that they have manufactured at the end of their lives for re-cycling / disposal. Any costs incurred by the manufacturers are being passed on to purchasers as part of new car prices.

Increasingly products are being re-conditioned or re-manufactured, to bring them up to as new (or in some cases, better than they were when originally new) condition. Commercial jet aircraft are normally almost completely re-built when they reach an age of about 15 years. This is cost effective for a variety of products as well as saving on raw materials and disposal. However apart from the example of aircraft above and some applications involving automotive components, the re-conditioning / re-manufacturing industry is still in its infancy and tends to consist of smaller companies, who are not always as efficient or as knowledgeable as the original large scale manufacturers. Environmental pressures seem certain to cause this sector of industry to grow.

The need to effectively recycle the maximum content of products is having an effect on the design process. Steel bodied vehicles have been fairly effectively recycled for many years, but the increased use of lighter materials, especially plastics, has complicated this. Plastic parts are now normally marked with an identification indicating their type / appropriate recycling process. Plastic parts in cars are increasingly being designed so they can be removed very quickly at the dismantling stage. Recycled trim plastic can be incorporated into bumpers and mud flaps. Unfortunately, there is still no commercially successful method of re-cycling tyres, and large tyre dumps can be found in most industrial countries.

Increasingly design engineers will have to consider how their designs, and the materials that they will be manufactured from, could be re-manufactured and recycled as this will affect the 'cost of ownership' of the product.

Further Reading - 'The Engineering Design Process', chapter 9., by A Ertas and J C Jones, John Wiley and Sons Inc., 1993.

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David Grieve, 18th March 2009, (original: 24th May 1999).