Analysis of Energy Use Figures 14.5 and 14.6 show general diagrams of energy use in a manufacturing process. Figure 14.4 is a specific example of Figure 14.5. With the recycling of the prompt scrap, the energy use is reduced, and is given by Equation 14.1 in the text. The greatest energy efficiency is obtained, of course, by designing the process to create as little prompt scrap as possible. Now the equation for the energy required per unit of product is Equation 14.2.
Fossil fuels are finite.
Their use does not constitute sustainable practice. Let's examine each fuel. For each Gte of Carbon burned, 0.47 ppmv of CO2 is distributed to the earth's atmosphere. Significant use of the earth's coal resource will significantly increase the CO2 concentration of the atmosphere. Coal is generally regarded as the dirtiest of the fossil fuels - gaseous and particulate emissions are significant.