Reducing the energy and greenhouse gasses ‘embodied’ in aggregate improves sustainability.
by Bill Langer
To some, the title of this article might sound like a sequel to the 1984 movie Ghost Busters, conjuring up images of three crazy scientists sucking demonic energy into their futuristic proton packs. Not to worry; embodied energy is not scary – it is part of sustainability.
The energy used to turn anything into a product, such as bedrock or a gravel deposit into aggregate, is referred to as ‘embodied energy.’ One goal of sustainability is to reduce the energy and associated greenhouse gasses embodied in manufactured products.
A number of energy-consuming activities contribute to the embodied energy of aggregate including prospecting for reserves; site preparation; constructing processing facilities; drilling, blasting, and excavating material; transporting material to the processing plant; crushing, screening, and washing; dust collection; sand classification; stockpiling; and load-out of the final aggregate products.
Some energy consumption does not apply to the embodied energy of aggregate. For example, the energy to manufacture crushers, screens, loaders, and so forth belongs with the equipment; and the energy to transport aggregate to the construction site belongs with the construction project.
So, how much energy is embodied in a ton of aggregate? Energy consumption ranges from 6 to 139 kilowatt hours per ton of aggregate produced. The actual consumption is dependent on factors including the size of the operation; geologic setting and type of rock or gravel being mined and processed; amount of drilling or blasting required; plant layout; type, efficiency, and maintenance of equipment being utilized; and experience and training of the plant manager, drillers, blasters, and other equipment operators.
You will be happy to hear that aggregates actually have a fairly low embodied energy. According to folks from the Centre for Building Performance Research in New Zealand, the average embodied energy, in kilowatt hours per ton, is 8 for gravel and 16 for crushed stone. For comparison, there are 750 kilowatt hours per ton of embodied energy in brick. Gypsum plasterboard and kiln-dried pine dimension lumber each has more than 2,000 kilowatt hours per ton of embodied energy.
You might want to read the January 2009 issue of Aggregates Manager to learn some ways to reduce fuel consumption and lower the embodied energy in aggregate. Some other ways to reduce embodied energy include the following:
- Increase blasting efficiency and create appropriately sized crusher feedstock by matching drilling and blasting to the geologic conditions and the rock being processed;
- Increase efficiency of in-pit truck transport of material by maintaining haul roads, reducing idle times of trucks, and utilizing engine idle management systems;
- Increase production efficiency by matching the feed rate to the crusher and matching motors (e.g. variable speed drive motors) to the equipment being used;
- Optimize equipment performance by using ‘smart’ crushers and screens that monitor equipment and transmit performance data to the operator or equipment manufacturer for remote problem solving;
- Reduce pumping costs by using geophysical data to identify water-filled conduits and grouting those conduits to restrict groundwater flow into the quarry; and
- Reduce overhead by improving lighting design and retrofitting indoor and outdoor lighting to include energy efficient lamps and ballasts.
Future technology may use rapid heating and cooling of quarried rock prior to crushing, which would promote rock fracturing, requiring less energy to crush the rock. To make this process viable, inexpensive, efficient tools to heat the rock, such as microwave or ultrasound equipment, need to be developed.
This makes me think that the image of three crazy scientists sucking energy out of rocks with some futuristic piece of equipment may be pretty accurate after all.
Who ya gonna call? ROCK BUSTERS!
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