Energy intensity for a total site

Equation (2.8) can be generally applied to different scenarios for power supply such as power import, on-site power generation from back pressure and condensing steam turbines as well as from gas turbines, which are discussed in detail in Chapter 3. 

By converting different energy forms to their fuel equivalent, process energy intensity in equation (2.3) can be revised to give 

To calculate the energy intensity index for the whole site, aggregate energy intensity could be defined simply as the ratio of total energy in fuel equivalent divided by total activity  

However, there is a problem here with this simple aggregate approach Although energy in fuel equivalent is additive, feeds (F) are not because processes usually have different feeds with very different compositions. In other words, the problem with equation (2.10) is the dissimilarity in feeds, which cannot be added without treatment. 

To overcome this dissimilarity problem in feeds, we could think of a reference site with energy intensity for each process known in prior. Thus, the total amount of energy use could be calculated for the reference site, as the summation of the energy intensity for the reference processes. Let us derive the mathematical expressions along this line of thought. 

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